Bivalve Abstracts 1999

BIOLOGY & EVOLUTION OF THE BIVALVIA

An International Meeting to Focus Solely on the Bivalvia | 14 -17th September 1999

Meeting Volume and Abstracts (scroll down)

The volume from this meeting is available to purchase on-line from The Geological Society.
Alternatively contact:

Geological Society Publishing House
Unit 7 Brassmill Enterprise CentreBrassmill Lane
Bath
BA1 3JN
UK
Tel UK+1225 445046
Fax UK+1225 442836

cover1cover2
ABSTRACTS
There follows, by request, a list of abstracts from the above meeting in alphabetical order. Thanks are due to Liz Harper and John Taylor, amongst others, for making the meeting such a success.

The Aberrant Jurassic Bivalve Opisoma: How did it Function?
Martin Aberhan

Museum für Naturkunde, Institut für Paläontologie, Invalidenstr. 43,
D-10115 Berlin, Germany. E-mail: mart@rz.hu-berlin.de

The aberrant bivalve Opisoma is represented in the Lower Jurassic (Middle Toarcian) of northern Chile by O. excavatum Boehm. Its very unusual morphology is characterized by a laterally strongly compressed shell, a very prominent posterior ridge and a very massive, ventrally elongated hinge plate. Lack of modern morphological counterparts for comparison has led to some confusion regarding the orientation of the valves in Opisoma, the position of the ligament and the site of adductor muscle attachment. The excellently preserved Chilean specimens allow to disentangle some of these confusions. What remains open to debate, however, is the opening mechanism. As Opisoma does not exhibit a clear ligamental area there is a possibility that the ligament has been lost completely in adults. This raises the question whether the valves were opened by muscles. However, the only muscle scar recognized in Opisoma seems to belong to a posterior adductor muscle rather than a “diductor” muscle. Opisoma excavatum is best interpreted as an epibenthic to partly buried species that rested on the anterior area of both the left and the right valve, and maintained its plane of commissure in a vertical position. It became stabilized by weight (extreme shell thickening and large size) and by form (broad triangular cross-section). Apparently, it evolved directly from shallow infaunal ancestors into the niche of edgewise recliners. Various independent lines of evidence suggest that O. excavatum is a potential candidate for palaeophotosymbiosis. Among these are: large size; thick shell; high skeleton-to-body ratio; adoption of an epifaunal life habit in an otherwise shallow infaunal stock; and palaeoenvironmental considerations. However, the apparent lack of microstructural adaptations to light transmission in a very thick shell is a good reason to be doubtful about a photosymbiotic way of life.
The Function of Freshwater Mussels (Bivalvia: Unionoida) in Aquatic Ecosystems

David C. Aldridge

Aquatic Ecology Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, U.K. E-mail: d.al@zoo.cam.ac.uk

The international declines and extinctions of freshwater mussels are widely documented and have resulted in the threatened unionoid fauna of many countries being made a conservation priority. What is less widely appreciated is that mussels perform a number of important roles in freshwater ecosystems which suggest that declines in even the common species could have important knock-on effects to the rest of the biota. For example, suspension feeding by mussel beds can reduce turbidity and modify plankton communities; mussel glochidia larvae are important parasites of some fish; mussels function as obligatory hosts to bitterling fish and Unionicola mites; external surfaces of mussels can be an important site of attachment for sponges, zebra mussels and even barnacles. This paper reviews these roles and discusses how declines in mussel communities can be controlled.

Extinction and Radiation of Bivalves in the Late Devonian

Michael R. W. Amler

Institut für Geologie und Paläontologie der Philipps-Universität Marburg, Abt. Invertebraten-Paläontologie, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
E-mail: aml@mailer.uni-marburg.de

The phylogenetic development of the Bivalvia during the Devonian is characterized by a distinctive diversification of many Early Palaeozoic taxa culminating in the Middle Devonian. However, the Kellwasser Crisis near the end of the Early Late Devonian marks a major break in bivalve evolution. This development is closely linked with the ecological evolution within bivalves corresponding with the relation to their specific habitats and the general diversification of ecological niches until the end of the Frasnian. The Early and Middle Famennian is generally void of diverse bivalve faunas. Again, close relationships to ecological and biofacies conditions are observable. Several taxa which had their acme during Early and Middle Devonian time, e.g. Actinodesma, Gosseletia, Pseuda-viculopecten, some pterinopectinids, Paracyclas, Cardiola and Buchiola, decreased dramatically during the Famennian and became extinct at the end of the Devonian. Other taxa of uncertain systematic position and partly unknown life habits disappeared already during the early Famennian, e.g. Praecardium, Opisthocoelus, Prosochasma, Loxopteria, Carydium, Prosocoelus. But, in contrast to earlier views, a new diversification of bivalves started already with the Late Famennian transgression (“Strunian”). Most of these taxa display “modern”, i.e. Late Palaeozoic, characters, crossed the Devonian/Carboniferous transition and reached a maximum in diversification during the Early Carboniferous. Important members of this radiation phase are pteriomorphs of the genera Aviculopecten, Limipecten, Fasciculiconcha, Streblochondria, Streblopteria, Euchondria, Undopecten, Pernopecten, as well as Prothyris, Edmondia and other members of the Anomalodesmata. In contrast, some other taxa of the pteriomorphs and most palaeotaxodonts display no diagnostic relationships to earlier or later faunas. They evolved from a diverse group of Devonian ancestors and persisted across the D/C boundary with Dinantian descendants, although detailed lineages are unclear, e.g. Leptodesma and Leiopteria among the pterineids, both displaying indistinctive or habitat controlled morphology. The same applies to the Palaeotaxodonts which were unaffected by global or regional changes during that interval and link the Devonian ancestors with their Carboniferous descendants. In summary, the bivalve fauna of the Latest Devonian (“Strunian”) exhibits a transitional character from the Devonian to the Carboniferous with a successive evolutionary transition across the D/C boundary rather than a sharp faunal break whereas a distinctive extinction event occurred during the Kellwasser Crisis near the Frasnian/Famennian boundary. Consequently, most Late Palaeozoic taxa originated already in the late Devonian rather than after the D/C boundary.
Phylogeography of Two Pearl Oysters Pinctada margaritifera and P. mazatlanica using Mitochondrial Markers

Sophie Arnaud(1), F. Bonhomme(1) and F. Blanc(2)

(1) Laboratoire « Génome, Populations, Interactions » Station Méditerranéenne de l’Environnement Littoral, 34200 Sete, France. E-mail: S-ar@crit.univ-montp2.fr
(2) Laboratoire de Zoogéographie, Route de Mende, 34199 Montpellier Cedex 5, France

We studied the genetic variability of two pearl oysters species, Pinctada margaritifera, which is ranging from Indian Ocean to Central Pacific, and P. mazatlanica which is found on American coasts from North Mexico to North Peru. P. mazatlanica is regarded either as a subspecies of P. margaritifera, or as a distinct species on the basis of morphological criteria. Allozymic data performed previously showed a close relationship of these two entities and led to the hypothesis that P. mazatlanica results from the colonisation of the American coasts by P. margaritifera cumingi from Polynesia. To test this hypothesis and give a further insight in the taxonomical status of the two taxa, we studied the genetic variation within and among populations of P. mazatlanica from North Mexico to Panama Pacific coasts, and of P. margaritifera cumingi from Cook to Marquesas Islands using the restriction polymorphism of two mitochondrial DNA genes (12S and Cox). A strong global structuring was observed among samples of P. mazatlanica, whereas at the same geographic scale, none or little differentiation was evidenced for P. margaritifera. The lack of common restriction haplotype did not permit however to ascertain the links between the two taxa. Nevertheless, the RFLP characterisation of P. margaritifera from Mauritius in the Indian ocean showed a greater genetic proximity of P. margaritifera and P. mazatlanica from central and eastern Pacific than these are from the Indian ocean subspecies. This would speak in favour of a direct link between the Pacific taxa, but raises the question of the taxonomical status of P. margaritifera at the scale of its whole range.
Naticid Predation on the Shells of Middle Miocene Corbulids – A Comparison (Ipolydamsd, Börzsöny Mountains, Hungary

Dávid Árpád

Kroly Eszterhzy Teachers’ Training College, Department of Geography, Eger, Hungary.
E-mail: dav@gemini.ektf.hu

Naticid gastropod predation on corbulids is described to be unusual because of low rate of success and lower frequency than predicted by a net energy maximization model. It is attributed to the conchiolin layers within the valves acting as an effective barrier to chemical boring by predatory gastropods. In this study naticid – prey interaction has been examined in the case of two corbulid species – Corbula (Varicorbula) gibba Olivi and Corbula carinata Dujardin. Borehole site selectivity, prey size selectivity and degree of predation success have been compared. Boreholes were most frequent on the right valves in the case of both species. The occurrence of incomplete boreholes was more significant on the tests of C. gibba. The ratio of multiplied borings was higher on the shells of C. gibba. There were no significant differences between the two species regarding site selectivity and prey size selectivity.

Unifying Principles of Particle Processing Mechanisms in Bivalves

Peter G. Beninger

Laboratoire de Biologie Marine, Faculté des Sciences, Université de Nantes, Nantes 44322 Cédex, France. E-mail: Pete@sut.univ-nantes.fr

Despite the observed diversity of particle processing modes in Bivalves, unifying principles have emerged from new observational techniques and intensive study over the past decade. Pallial organ anatomy determines the water/particle flow characteristics and processing routes, cilia type determines particle – pallial organ interaction, and mucus type determines the nature of particle processing. We will focus on effector (cilia and mucus) types used in the processing sequence of capture, transport, selection, ingestion/rejection. In bivalves possessing laterofrontal cirri (the vast majority), laser confocal observations demonstrate direct cilia-particle interaction at the capture point; transport involves simple cilia and mucus in all bivalves studied, either as classical mucociliary transport or as a modified mucociliary-hydrodynamic transport. Physical and biochemical fluidization of the mucus-particle strands occurs on the palps in species which use this organ for selection (the vast majority). Rejection of excess volume or negatively – selected material is universally mucociliary, involving acidic mucopolysaccharides and counter-current transport. Elevation of rejecta and mucociliary transport above the general mantle epithelium is the rule in all species with gill ventral particle grooves (again, the vast majority). A specific type of cilium is usually involved. Ingestion takes place within a fluidized mucus slurry. Unifying principles continue to be determined, based on the effectors – cilia and mucus – of particle processing in bivalves.

This paper will be given as part of the Feeding Workshop.

Bivalve Gill Abfrontal Ciliation and Mucocyte Types: what they convey about the evolution of this organ

Peter G. Beninger(1) and Suzanne C. Dufour (2)

(1) Laboratoire de Biologie Marine, Faculté des Sciences, Université de Nantes, Nantes Cédex 3, France. E-mail: Pete@sut.univ-nantes.fr
(2) Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, U.S.A.

The lack of fundamental data on the abfrontal surface of bivalve gills has prompted a comparative study of cilia and mucocytes on this surface. These features have been studied by scanning electron microscopy and histology on eight species of bivalves, representing seven families and the four major gill types (Mytilus edulis, Modiolus modiolus, Arca zebra, Placopecten magellanicus, Crassostrea virginica, Spisula solidissima, Mya arenaria and Mercenaria mercenaria). Inter-species variations were found; gradients in the numbers and diversity of cilia and mucocytes were observed for each gill type. These results indicate that the abfrontal surface had a primitive role in mucociliary cleaning (prior to filament folding), and that the cilia and mucocytes observed in contemporary species are vestigial. In general, the degree of abfrontal cilia and mucocyte loss parallels the degree of evolution of the gill: eulamellibranchs have fewer abfrontal cilia and mucocytes than homorhabdic filibranchs. The data are consistent with the interpretation that the loss of the primitive mucociliary cleaning function gave rise to two evolutionary outcomes: (1) selective pressures led to the reduction in numbers and types of abfrontal mucocytes and cilia; and (2) abfrontal mucocytes were retained as they assumed new functions in water flow.
Reproductive Output in Macoma balthica in the Wadden Sea: do they follow an optimal strategy?

Jan Beukema and Pieter Honkoop

Netherlands Institute for Sea Research, PO Box 59, 1790 Den Burg, Texel, The Netherlands. E-mail: jsr@nioz.nl

Annual reproductive output in individual females of the tellinid bivalve Macoma balthica (L.) varies strongly from 0 to about 100,000 eggs. Expressed as a proportion of the ash-free dry weight (AFDW) of the soft parts, it varies from 0 to about 33% (Honkoop et al. 1999: “Reproductive investment in the intertidal bivalve Macoma balthica” J. Sea Res. 41, 203-212). This variation is strongly related to the “condition” of the animals, expressed as the body-mass index (BMI), i.e. AFDW divided by the third power of shell length. Lean animals with a BMI of 5.6 mg cm-3 or less do not spawn any eggs. At the other extreme, maximal proportions of about 30% of AFDW are reached at BMI values > 10 mg-3. Long-term monitoring (> 20 y) of Macoma densities at Balgzand (a tidal-flat area in the westernmost part of the Wadden Sea) revealed that the proportion surviving to the next year was lower at low than at high BMI at the start of the spawning season (ranging from about 0.25 at BMI=5.6 to about 0.65 at first spawning, viz. both as an immediate response (determining the proportion of the weight spawned as eggs) and as a delayed response in following years (via BMI-dependent proportions of the animals spawning also in subsequent years). Therefore, a trade-off situation exists between the present and the future spawning occasions. Any further reduction of BMI by a larger immediate spawning would result in lower survival and thus lower outputs in future years. It may be expected that animals will optimize total lifetime reproductive output. Lifetime reproductive outputs were calculated at different strategies on the first spawning occasion, ranging from postponement to the next year (0% output at all BMI values) to maximal output (all mass above BMI=5.6 or 30% of AFDW at all BMI>8.0). It is concluded that the realized strategy of an increase of reproductive output with “condition” is close to an optimal one.
Marine Bivalves of the Florida Keys: discovered biodiversity

Rüdiger Bieler (1) and Paula M. Mikkelsen (2)

(1) Department of Zoology, Field Museum of Natural History, Roosevelt Road at
Lake Shore Drive, Chicago, Illinois 60605-2496, U. S. A. E-mail: bie@fmnh.org
(2) Department of Invertebrates, American Museum of Natural History, Central
Park West at 79th Street, New York, New York 10024-5192, U. S. A.
E-mail: mik@amnh.org

The Florida Keys island group at the southernmost tip of the continental U.S. supports a remarkably diverse marine malacofauna. Surprisingly, after a century of popular and professional shell collecting, the molluscs have never been comprehensively assessed. Although best known for its coral reefs, the Keys comprise about 10,000 km2 of marine habitat, and include hypersaline ponds, mangrove thickets, seagrass meadows, muddy tidal channels, sandbars, and deep sand plains. This molluscan survey (in part addressing the needs prompted by establishment of the Florida Keys National Marine Sanctuary in 1991) compiled from over 200 original collections, 4,000 museum lots, and 3,000 literature records, revealed over 1,300 molluscan species, including more than 300 bivalves. These represent a wide taxonomic diversity -50% of recognized families and 70% of superfamilies. Systematic scrutiny has shown several cryptic species pairs, commonly known under a single taxonomic name, but morphologically different and associated with different habitats (e.g., estuarine Florida Bay versus oceanic coral reefs). Community analyses show roughly equal proportions of infaunal and epifaunal species, with the latter including “coral reef-important” borers and cementers. Within-Keys distributions include one-third of species ranging the full length of the island chain, one-third so far recorded from a single zone (Upper, Middle, Lower, Tortugas), and one-third overlapping two or more zones. Species ranges show ca. 50% of Keys bivalves considered “wide ranging” both north and south, but 85% of the remainder decidedly tropical in distribution. Historical records indicate little species turnover, although habitat shifts from natural to artificial substrata are evident.
On Becoming Sessile: Evolutionary Relationships among the Genera in the Cemented Freshwater Bivalve Family Etheriidae (Bivalvia: Unionoida)

Arthur E. Bogan (1) and Walter R. Hoeh (2)

(1) North Carolina State Museum of Natural Sciences, P.O. Box 29555, Raleigh, NC
27626, U.S.A. E-mail: Arth@mail.ENR.STATE.NC.US
(2) Department of Biological Sciences, Kent State University, Kent, OH 44242, U.S.A.

The family Etheriidae (freshwater oysters) has been recognized as a distinct taxon for well over 160 years. The relationships of this family to other unionoid families and its constituent genera have been debated. Many malacologists recognize three genera in the Etheriidae: Acostaea (Columbia, South America), Pseudomulleria (India), and Etheria (Africa and Madagascar). Mansur and da Silva (1990) have recently supported this monophyletic view of the Etheriidae. However, Starobogatov (1970) placed the three genera into distinct families: Acostaea in the Mulleriidae, Mullerioidea along with the Mycetopodidae, Etheria remained in Etheriidae, and Pseudomulleria in Pseudomulleriidae, both placed in the Etherioidea. Similarly, Bonetto (1997) has placed Acostaea in the Acostaeinae in the Mycetopodidae, Etheria in the Etheriinae and Pseudomulleria in the Pseudomulleriinae, both in the Mutelidae. Thus, the works of Starobogatov (1970) and Bonetto (1997) contradict the monophyly of the Etheriidae by suggesting instead that the Etheriidae is a polyphyletic assemblage. These conflicting views on the evolutionary relationships surrounding the etheriid genera hinder the development of a basic understanding of the circumstances involved in the evolution of the sessile habit in freshwater bivalves. A fundamental question is: did the sessile habit in unionoids evolve once or multiple times? A monophyletic Etheriidae would support the former hypothesis while a polyphyletic Etheriidae would support the latter. To evaluate these possibilities, we have conducted phylogenetic analyses of mitochondrial DNA sequences (COI) to examine the relationships of the 3 etheriid genera to representatives of 27 other unionoid genera. Preliminary analyses firmly place Acostaea within a clade of Anodontites species, currently in the Mycetopodidae.
Mitochondrial and Nuclear DNA Phylogeography of Two Cupped Oysters Crassostrea gigas and Crassostrea angulata

Pierre Boudry and Arnaud Huvet

IFREMER, Station de La Tremblade, Ronce les Bains, BP 133, 17390 La Tremblade, France. E-mail: pboudry:ifremer.fr

The taxonomic status of Crassostrea angulata and Crassostrea gigas has long been a matter of controversy. Morphological and physiological similarities, as well as homogeneity in allelic frequencies on allozymes between the populations of the two taxa, lead most authors to suggest to regroup of the two within the same species. European and Asian populations of C. gigas and C. angulata have been studied using microsatellite and mitochondrial DNA markers. The analysis of genetic distances and the distribution of allelic and haplotype frequencies revealed a differentiation between the populations of C. gigas and C. angulata. The data allowed the construction of Neighbor-joining trees for each of the two types of markers. Similar topologies appeared with data on both genomes showing two clusters, but mitochondrial DNA presented much higher genetic differentiation among taxa than microsatellites. The first cluster included the French and Japanese populations and the second the Taiwanese and Portuguese populations. The Asiatic origin of Crassostrea angulata taxa is therefore confirmed. Despite their history, European populations of C. angulata did not show any significant reduction of variability compared to Asian populations.
The Effect of Reproduction on Locomotor Performance and Muscle Metabolic Capacities in the Scallop Chlamys islandica

Katherina Brokordt, John Himmelman and Helga Guderley

Dépt. de Biologie, Université Laval, Québec, G1K 7P4 Canada.
E-mail: Kath@girog.ulaval.ca

In scallops, during gametogenesis biochemical reserves such as glycogen and proteins are mobilized from the adductor muscle towards the gonad. This mobilization of material is likely to diminish the metabolic capacities of the adductor muscle and thereby the scallops’ escape response. Scallops must make a trade-off between a loss in their capacity to escape from predators and the availability of materials for gametogenesis. We examined the escape response and the recuperation from exhausting exercise in adult scallops Chlamys islandica sampled at different reproductive stages (immature, mature before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoarginine content, as well as the levels of enzymes that participate during muscle contraction and recovery, such as glycogen phosphorylase (GP), phosphofructokinase (PFK), pyruvate kinase (PK), octopine deshydrogenase (ODH), arginine kinase (AK), and citrate synthase (CS). We also measured the oxidative capacity of mitochondria isolated from the adductor muscle. Immature animals recovered their initial swimming capacity within 6 h, but mature and spawned scallops needed 12 an 18 h respectively. The number of claps (24-26) as well as phosphoarginine and AK levels were similar during the different reproductive stages. However, mature and spawned animals showed a decrease of GP, PFK, PK, ODH and CS levels and a deterioration of oxidative capacity of muscle mitochondria as well as a marked decrease of glycogen contents. Therefore, during gonadal maturation and spawning, C. islandica did not change its clapping capacity, but decreased its glycolytic and aerobic recuperation after an exhausting burst exercise, most likely due to the decreased metabolic capacity of the adductor muscle.
Reproduction of the Hermaphroditic Brooding Clam Corbiculina australis in New South Wales: a light and electron microscope study

Maria Byrne(1), Harriette Phelps(2), Tony Church(3) and Jaimie Potts(3)

(1) Department of Anatomy and Histology F13, University of Sydney, NSW 2006, Australia. E-mail: mby@anatomy.usyd.edu.au
(2) Department of Biological and Environmental Sciences, University of the District of Columbia, 4200 Connecticut Avenue, Washington, D.C. 20008, U.S.A.
(3) NSW EPA, Locked Bag 1502, Bankstown, NSW 2200, Australia

The freshwater clam Corbiculina australis is an important component of the macrobiota of the river systems of southeastern Australia. Reproduction of two populations of this clam in the Nepean River, NSW was investigated to document their gametogenic cycle, larval morphology and to determine when they incubate embryos in their gill marsupia. C. australis is a simultaneous hermaphrodite and broods its young in the inner demibranch. The gonads are ovotestes with oogenic and spermatogenic regions in each ascinus. The sperm are biflagellate, a condition unique in the Bivalvia to triploid asexual corbiculids. Gametogenesis was continuous and did not exhibit a seasonal pattern. In contrast, spawning and incubation of embryos was limited to the warmer months of the year. Embryos were present in the marsupia for up to eight months of the year from mid spring to late summer. In most years brooding started in October and was finished by May of the following year. C. australis develops through a highly modified veliger larva. These larvae have a vestigially ciliated velum which is not used for swimming or particle capture. The velum is covered by microvilli and it is suggested that the velar epithelium may be specialised for nutrient uptake in the marsupial environment. C. australis produces several clutches each year and the young are released as advanced juveniles with a well-developed foot. Reproductive output was strongly influenced by habitat trophic status. The suite of life history traits exhibited by C. australis: hermaphroditism, potential for self-fertilization/androgenesis, brooding progeny to the crawl-away juvenile stage and a high reproductive output, provide for rapid recolonization and population growth in this clam which typically inhabits disturbance prone sandy lotic habitats.
Comparison of Morphological and Molecular Evidence on the Phylogeny of the Bivalvia

David C. Campbell

Department of Geological Sciences, CB 3315 Mitchell Hall, UNC-Chapel Hill, Chapel Hill, NC 27599-3315, U.S.A. E-mail: biva@email.unc.edu

Although DNA sequencing potentially provides enormous amounts of new data for phylogenetic analyses, DNA-based studies so far have not reached a consensus on the phylogeny of the Bivalvia, and often yield results in conflict with the consensus from morphological data. Likewise, morphology-based studies are often in conflict with each other. The present study analysed the entire 18S gene sequence for representatives of all living orders and a wide range of superfamilies and compared this to published morphological analyses and unpublished data, including revisions of the published analyses. The DNA-based analyses provided greater agreement with morphological data than many earlier studies, probably reflecting the increased taxonomic coverage and longer DNA sequences. All subclasses and almost all orders were recognized as monophyletic. Myoida, however, appears to be polyphyletic, in agreement with some morphology-based hypotheses. Likewise, many of the relationships among the orders and subclasses suggested by the DNA have been previously proposed on the basis of morphological studies. However, some conflicts remain to be settled by further study.
Phylogenetic Significance of Shell and Ligament Micro-Structure in Silurian Bivalves from Gotland, Sweden

Joseph G. Carter and David Campbell

Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599-3315, U.S.A. E-mail: cla@email.unc.edu.

Recrystallized bivalves from the Upper Silurian Mulde beds of Djupvik, Gotland, contain excellent relict shell microstructure, including mineralized ligament layers. This preservation may reflect recrystallization under slightly reducing conditions in which oriented internal organic matrices are initially preserved in the diagenetic calcite. Etching the calcite reveals their former positions. The Mulde praenuculids, nuculids, and malletiids were characterized by a well-mineralized, submarginal simple ligament, and the nuculids also had a well-mineralized internal resilium. Both nacreous and non-nacreous nuculids had appeared by this time. The ctenodontid Tancrediopsis foreshadows acharacid solemyoideans in its combination of a short, cylindrical, parivincular ligament, a nacreous interior, and possibly also an organic-rich outer shell layer. Colpomya and Aleodonta had nacroprismatic shells and multiple simple ligaments, thereby confirming a close prelationship between the Modiolopsoidea and the early Mytiloidea as well as the Pterioida and Cyrtodontoida. Except for the Mytiloida, Evyana is unique among early pteriomorphians in combining a duplivincular ligament with an entirely aragonitic, nacroprismatic shell.
A Mechanical Model for Rib Formation in Ostreiodea

Antonio G. Checa and Antonio P. Jiménez

Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain. E-mail: ach@goliat.ugr.es

Longitudinal ribs in bivalves run from the umbo to the margin; they are perpendicular to growth lines at the shell centre and become progressively more oblique towards the anterior and posterior ends. Each rib reflects the ontogenetic trajectory of the mantle sector forming it. Ostreoidea (Ostreidae and Gryphaeidae) do not match this pattern in that their ribs are perpendicular to growth lines throughout the whole shell. This implies that only in the shell centre are ribs truly longitudinal whereas towards the sides they curve lateralwards. Each rib is formed either by a laterally migrating mantle portion or by different portions of it. Oyster rib features are consistent with a mantle which extrudes perpendicular to the shell margin each time a new growth increment is to be secreted; upon extrusion the mantle margin increases its length disproportionately compared to the straight length of the shell margin, i.e., excluding the folds. This causes wrinkling along axes perpendicular to the margin, i.e., the lengthening direction. In this view, oyster ribs are purely mechanical structures whose number, size and position are not genetically fixed, but rather depend upon the mechanical properties of the mantle. This explains the high variability and irregularity of oyster ribbing patterns. This mode of rib construction contributes to phenotypic plasticity, which enables Ostreoidea to encrust a large variety of irregular substrata. The above model is supported by the homogeneous nature of the oyster mantle, unlike other ribbed bivalves in which each rib is formed by a specialised mantle protrusion.
A Second Look at Eastern Pacific Recent Species of the Bivalve Genus Gari

Eugene V. Coan

Department of Invertebrate Zoology, California Academy of Sciences, Golden Gate Park, San Francisco, California 94118-4599, U.S.A. Mailing address: 891 San Jude Avenue, Palo Alto, California, 94306-2640, U.S.A; also Research Associate, Santa Barbara Museum of Natural History and Los Angeles County Museum of Natural History.
E-mail: gene@sierraclub.org

A study has been conducted of the type and other material of the Recent eastern Pacific species of the bivalve genus Gari. There are seven species of Gari (Gobraeus). (1) Gari (G.) californica (Conrad, 1849) (synonyms: Psammobia rubroradiata Carpenter, 1864; P. lilacina Wilkins, in Palmer, 1958 [in synonymy]) occurs from Kachemak Bay, Alaska, to Bahía Magdalena, Baja California Sur, Mexico, but with a gap between Puget Sound and Mendocino County, California. Based on the material currently available in the United States, it cannot be distinguished from the northwestern Pacific G. kazusensis (Yokoyama, 1922), which is also regarded as a synonym, along with G. k. atsumiensis Hayasaka, 1961. (2) Gari (G.) fucata (Hinds, 1845) (synonym: Siliquaria edentula Gabb, 1869), occurs from Ventura County, California, to Punta Eugenia, Baja California Sur, Mexico, and perhaps as far south as Bahía Magdalena. (3) Gari (G.) lata (Deshayes, 1855) (synonym: Psammobia regularis Carpenter, 1864), occurs from Bahía Magdalena, Baja California Sur, Mexico, throughout the Gulf of California, south to Santa Elena, Ecuador. Records of Gari regularis from northern Baja California are based on misidentified small, elongate, inflated specimens of G. californica. (4) Gari (G.) maxima (Deshayes, 1855) occurs from Mazatlán, Mexico, to Panama. (5) Gari (G.) panamensis Olsson, 1961, occurs from the central Gulf of California to Playas, Ecuador. (6) Gari (G.) solida (Gray, 1838) (synonyms: Psammobia solida Philippi, 1844; P. crassa Hupé, 1854), occurs from Arica to Rio Inio, Chile. (7) A probable new species of Gari (G.) occurs in the Galapagos Islands, thus far represented by only a single, small, broken specimen. An eighth species, Gari (Dysmea) helenae Olsson, 1961, occurs from Laguna Ojo de Liebre, Baja California Sur, Mexico, throughout the Gulf of California, south to Isla Salango, and the Galapagos Islands, Ecuador. Its relationship to the western Atlantic Gari circe (Mörch, 1876) and G. linhares Simone, 1998, remain to be resolved. Several lectotype designations will be made, and a list will be provided of New World Recent and fossil taxa that have been placed in Gari.
Phylogeny: The Key to Bivalve Taxonomy

John C.W. Cope

Department of Earth Sciences, Cardiff University, PO Box 914, Cardiff CF1 3YE, U.K.
E-mail: cope@cardiff.ac.uk

In the 30 years since publication of the bivalve Treatise, important new faunas have been described, from the early and mid Cambrian and from the early and mid Ordovician. These contain significant new forms, including some long-ranging intermediate groups, that indicate the relationships between the principal bivalve clades. We now know that the earliest bivalves were palaeotaxodonts, resolving the controversy over the primitive bivalve dentition, and that the major phase of bivalve diversification followed on from the evolution of the Subclass Autobranchia, in the latest Cambrian or earliest Ordovician (a time interval that coincides with a major hiatus in the bivalve record). The principal division of the Class is into two subclasses, Protobranchia and Autobranchia; links between the two can be demonstrated in the early Ordovician. Major divisions of each subclass are recognised as superorders. Within the Protobranchia, the Palaeotaxodonta developed specialist food-gathering palps and an enlarged foot. They diversified to produce distinct forms living symbiotically with sulphur-oxidizing chemoautotrophic bacteria; this allowed colonization of soft substrates and produced two stocks: the deeply infaunal anteriorly elongate solemyoids (Lipodonta) and the semi-infaunal and epifaunal Cryptodonta. The Autobranchia, initially identified by strongly asymmetrical hinges, diverged in three directions, each characterized by distinctive hinges. The Anomalodesmata developed a strong ligamental insertion and largely lost their dentition. The Trigonioids were characterized by denticulate teeth and rapidly regained greater symmetry, whilst the Heteroconchia, with a crossed-lamellar shell, bifurcated early into the glyptarcoids leading to the neotaxodonts and pteriomorphians, and the actinodontoids leading to the mainstream heteroconchs.
Evolution of Taxonomic Diversity Patterns in Marine Bivalves

J. Alistair Crame

British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, U.K.
E-mail: JAC@pcmail.nerc-bas.ac.uk

Bivalves have been fundamental to the development of our understanding of large-scale biodiversity patterns in the mariine realm. In particular, they have helped delineate steep latitudinal gradients in each hemisphere and high-diversity foci in the central American and Indonesian-Philippines regions, respectively. A new global compilation of some 29 regional bivalve faunas again picks out these patterns but suggests that there is in fact a considerable degree of north-south asymmetry. Whereas northern gradients tend to be steeper and more regular, southern ones are influenced by a more complex pattern of inter-regional variation. It is likely that bivalve latitudinal and longitudinal gradients have been formed by a combination of equilibrium and non-equilibrium processes. Amongst the latter, it is now clear that the steepest gradients occur in the youngest bivalve taxa. This relationship is particularly strong within the heteroconchs, the youngest, and largest, of seven major extant clades. It can be concluded that the Late Cretaceous – Cenozoic infaunalization of the Bivalvia was essentially a low-latitude phenomenon, and that many heteroconch groups have yet to become fully established within high-latitude and polar ecosystems. Observations on a series of fossil latitudinal gradients indicate that tropical high bivalve diversity has been consistently underpinned by infaunal taxa. A comparison of Late Palaeozoic, Mesozoic and Recent gradients gives some indication of the rate at which clades may have been displaced into high latitudes.
Evolution of Shape throughout the Lifespan of an Infaunal Bivalve Genus: Cenozoic Spissatella (Crassatellidae) from New Zealand

James S. Crampton(1) and Phillip A. Maxwell(2)

(1) Institute of Geological and Nuclear Sciences, P.O. Box 30-368, Lower Hutt, New Zealand. E-mail: .
(2) Bathgates Road, R.D. 10, Waimate, New Zealand

Spissatella is a moderately speciose genus of non-siphonate, shallow water Crassatellidae from the Late Eocene to Late Miocene of New Zealand and Australia. This study uses Fourier shape analysis to examine ontogenetic, intra-“populational”, and evolutionary changes in outline shape in 300 individuals from 20 collections spanning the Eocene to Miocene. Outline shape was probably a key target of evolutionary selection, given its relationship to speed and depth of infaunal burrowing and, therefore, survival in the face of predation and environmental perturbation.

Results demonstrate that, over a 20 Ma period, the greatest component of shape variation was related to ontogenetic development and that evolution in Spissatella was largely the result of heterochronic processes operating at the post-larval stage. Furthermore, size and shape covary and it appears that these two traits were not selected for independently: to vary shape, it was necessary to vary size, or vice versa. There was little evolution away from the basic ontogenetic plan and, where detected, such evolution may have been a consequenceof heterotopy (changes in the spatial patterning of growth fields). The basic ontogenetic plan is diagnostic at the generic level. The data also demonstrate that morphological variance is inversely correlated with water depth; that there is little evidence of morphological stasis at the sampling resolution; and that there are no long-term evolutionary trends in size or shape. Together, these results suggest that throughout the lifespan of this clade, evolution was dominated by gradual change in response to shifting environmental ranges and within strict developmental constraints.
Genetic Characterisation of Mytilus galloprovincialis Populations with Nuclear DNA Markers

Claire Daguin(1), François Bonhomme(1) and Philippe Borsa1(2)

(1) Laboratoire Génome, Populations, Interactions, UPR 9060 CNRS, Université de Montpellier II, Centre National de la Recherche Scientifique, 34200 Sete, France.
E-mail : dag@crit.univ-montp2.fr
(2) Institut de Recherche pour le Développement, Montpellier Station Méditerranéenne de l’Environnement Littoral, 1 Quai de la Daurade, F-34 200 Sete, France

The genetic relationships among Mytilus galloprovincialis populations over their world-wide range were investigated using polymerase chain reaction (PCR)-amplified nuclear DNA markers. We used long-range polyacrylamide gel electrophoresis for characterising a high level of intron-length polymorphism at the actin gene locus mac-1, the most polymorphic DNA marker known to date in Mytilus. Significant differences in allelic frequencies were observed between north-eastern Atlantic and Mediterranean M. galloprovincialis populations, but no variation was detected within either the Atlantic or the Mediterranean/Black Sea. M. edulis alleles were present at low frequencies in Atlantic M. galloprovincialis populations, and to a lesser extent in Mediterranean populations. Previous allozyme and morphological surveys have shown that M. galloprovincialis is also present in California, Northeast Asia, South Africa and Australia/New Zealand. The genotypic characterisation of non-European populations at locus mac-1 revealed that the origin of Korean M. galloprovincialis is the Mediterranean whereas the origin of South African M. galloprovincialis is the Atlantic. Californian M. galloprovincialis were found to be close to, although slightly different from, Mediterranean M. galloprovincialis. We also report for the first time the occurrence of M. galloprovincialis, of Mediterranean origin, in central Chile. All the foregoing M. galloprovincialis populations were also characterised at the polyphenolic adhesive protein gene locus Glu 5′, which is supposed to be diagnostic between M. edulis, M. galloprovincialis and M. trossulus. Glu 5′ data were generally in accordance with mac-1 data.

A Fresh Look at Jurassic Retroceramidae and their Mode of Life

Susana E. Damborenea (1) and Paul A. Johnston (2)

(1) Departamento Cientìfico Paleontologìa Invertebrados, Museo de Ciencias Naturales, La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina. E-mail: susa@mmance.cyt.edu.ar
(2) Royal Tyrrell Museum of Paleontology, Box 7500, Drumheller, Alberta, Canada T0J 0Y0. E-mail: pjoh@mcd.gov.ad.ca

The taxonomic relationships and life habits of retroceramids are reappraised on evidence from Middle Jurassic Retroceramus species from central western Argentina and elsewhere. The family Retroceramidae is removed from the Pteriomorphia and relocated within the Superfamily Inoceramoidea in the Subclass Cryptodonta because: a) details of the retroceramid ligamental area reveal a linear growing margin, as in inoceramids, and not sinusoidal, as in Isognomon; b) posterior pedal muscle scars are comparatively large, subcentrally placed, and well separated from the relatively small, distally placed posterior adductor, fitting the inoceramid and praecardioid patterns, not that of pteriomorphs; c) several species show geniculations of shell profile resulting from changes in shell convexity and ornament during ontogeny; and d) main ornament consists of pronounced comarginal rugae affecting both inner and outer shell surfaces. Shell shape and ornamentation indicate that Retroceramus species were orthothetic, probably semi-infaunal or epifaunal, and lived on mud-grade substrates in poorly oxygenated settings, as supported by taphonomic evidence. Occurrence of these bivalves with ammonoids only, or with few other benthonic megafauna, in deposits originated in dysaerobic environments suggests that retroceramids may have harboured as symbionts chemosynthetic sulphophilic bacteria, as already proposed for inoceramids on various grounds (isotopic, sedimentological, etc.) by other authors. Furthermore, peculiar modifications of the ventral region of some Retroceramus species studied, suggest a thin, flexible, ventral flap-like extension of the shell margin which might have been related to the presence of a ventral, sulphide-pumping organ.
Palaeogeographic Distribution Patterns in Upper Cretaceous Bivalves

Annie V. Dhondt

Department of Palaeontology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B – 1000 Brussels, Belgium. E-mail: dho@d5100.kbinirsnb.be

The Upper Cretaceous is a period of extensive transgressions. In the Cenomanian NW Europe was largely covered by shallow seas. The faunas from the Upper Greensand facies from S. England also occur in W. France, Belgium, Germany (Westphalia and Saxony), Czechia, Poland, Western and Eastern Russian Platform, Moldavia and into Central Asia.
Coeval transgressive pulses distributed mainly oysters on the northern margin of the Tethys, from the Paris Basin to Central Asia. Part of these strata contains rudists. Especially in the fore and back reefs of these rudist bioherms specific faunal associations are present (N. Italy and the Balkan). In Northern Africa (and Sicily) the Cenomanian is characterised by extensive oyster facies (also containing plicatulids, pectinids (Neithea and large Chlamys), limids). Many taxa extended from NW South America, from Mexico-Texas across N. Africa and W. Asia, into Central Asia. The Cenomanian/Turonian regression with its anoxic facies in less shallow deposits) resulted in the extinction of many bivalve taxa. Only progressively new taxa replace them from the Turonian onwards. In N. Europe White chalks appeared in the Turonian: a not very shallow deposit showing specific evolution between the Turonian and the Campanian (Lower Maastrichtian) (in pectinids (Chlamys, Microchlamys), limids (Plagiostoma, Limatula, Limea), spondylids and inoceramids (especially Mytiloides). In the Turonian – Campanian, in more littoral environments, oysters, pectinids (Neithea), limids (Ctenoides) and in the Tethys the evolution was different (example: N. Tethys deposits in the Gosau). The S. Tethys continued to have an oyster facies in shallow environments. The S. American faunas contained elements common with North Africa until the Campanian, but endemic elements already occur in the Santonian (?) Campanian Maastrichtian. In N. America a cosmopolitan fauna is known in the Albian-Cenomanian, but later the Western Interior, Texas and the Atlantic Coast contain more endemic elements. The W. Coast faunas from the Turonian onwards are Pacific, and closer to the Japanese and Eastern Siberian faunas.

New Perspectives on the Gills and Pallial Organs of Freshwater Mussels (Paleoheterodonta: Unionoida: Unionoidae)

Ronald V. Dimock, Jr (1), Richard A. Tankersley (2) and Maria Byrne (3)

(1) Department of Biology, Wake Forest University, Winston-Salem, NC 27109, U.S.A.
E-mail: dim@wfu.edu
(2) Department of Biological Sciences, Florida Institute of Technology, Melbourne, FL 32901, U.S.A.
(3) Department of Anatomy and Histology, University of Sydney, NSW 2006, Australia

Video endoscopy provides real-time in vivo visualization of the structure and function of pallial organs of bivalves that here-to-fore could not adequately be imaged. For example, insertion of an endoscope into the supra-branchial chamber enables viewing of the interior of gills, revealing 3-dimensional detail that previously could only be interpreted from histology or dissection. We have used this technique to examine the gills and associated structures of the Hyriidae, Margaritiferidae and Unionidae, families that exhibit the three larval brooding conditions of the Unionoidea. Endobranchous species utilize the inner demibranchs for the retention of developing glochidia, whereas tetragenous species employ all four, and ectobranchous mussels use the outer demibranchs. Differential use of gills as marsupia is accompanied by variation in the interlamellar tissue connections characteristic of the eulamellibranch ctenidium. Endobranchous hyriids have perforated interlamellar septa in the marsupial demibranch. The tetragenous margaritiferids have either simple interlamellar tissue junctions or obliquely oriented septa. Anodontine unionids have numerous vertical non-perforated septa in the marsupial demibranch. The separation of infra- from supra-branchial chambers is either partial via diaphragmatic septa (margaritiferids) or a perforate gill diaphragm (hyriids) or complete by the fusion of gills to the posterior mantle (unionids). In vivo imaging revealed the dynamic association of labial palps with the demibranchs. In addition, hyriids, unlike margaritiferids and unionids, are shown to have a prominent renal papilla adjacent to the genital opening in the supra-branchial space above the innner demibranch. These imaging techniques provide new insights for functional and phylogenetic considerations.

Videotapes from this study may be viewed during the Feeding Workshop.
Burying Depth of Macoma balthica represents a Flexible Anti-Predation Behaviour

Pim Edelaar (1,2) and Diliana Welink (2)

(1) Netherlands Institute for Sea Research, Texel, The Netherlands.
E-mail: edel@nioz.nl.
(2) Center for Ecological and Evolutionary Studies, University of Groningen, The Netherlands

Macoma balthica is a small tellinid that buries in soft sediment. Burying depth shows extreme variability, and the adaptive value of the variation was studied. Burying depth is usually explained in terms of a trade-off between food and safety, as deeply buried individuals supposedly are at smaller risk of predation, but suffer from a decrease in food intake. Our experiments show that individuals fixed at shallow depths grew more then those fixed at greater depths, and when food is provided, the individuals bury less deep. Individuals exposed to predator cues bury deeper, indicating a benefit of burying deeper when in danger of predation. Burying depth can be largely explained by the size of the individual. Up to a shell length of about 15 mm individuals bury progressively deeper, but from then onwards burying depth diminishes rapidly. Are these larger individuals in some way constrained? Both small and large individuals were exposed to either caged small or large Shore crabs (Carcinus maenas), or control empty cages. The large individuals did bury deeper when crabs were present, showing that such a constraint is not present. Interestingly, they increased burying depth mostly when the predator was a large crab. Small individuals already showed a large increase in burying depth when exposed to small crabs. Small crabs can open small individuals but cannot eat large individuals, whereas large crabs can. These experimental data confirm that burying depth is a trade-off between food intake and risk of predation. Such a flexibility in anti-predation behaviour will not only affect survival rates, but also growth and reproductive rates.
Correlation of Protein Synthesis with Morphological Changes during Metamorphosis of the Glochidia of Utterbackia imbecillis (Unionoida: Unionidae)
Ginger R. Fisher and Ronald V. Dimock, Jr.

Department of Biology, Wake Forest University, Winston-Salem NC 27109, U.S.A.
E-mail: mack@wfu.edu

The period of metamorphosis from glochidia to juvenile is a critical time in the life history of unionid mussels; however very little is known about the molecular and morphological changes that accompany this transition. Glochidia were isolated from gravid parental mussels and cultured in vitro through metamorphosis. The rate of RNA, DNA and protein synthesis was measured daily over the 8-day development period. There was a significant decrease in the rates of synthesis during metamorphosis as compared to pre-cultured glochidia and juvenile mussels. Once the animals entered the metamorphic period, the level of cell division and protein synthesis increased steadily for three days and then decreased dramatically between days three and four. The fourth day of metamorphosis was characterized by low rates of RNA, DNA and protein synthesis. From day four until the end of metamorphosis, the synthesis levels steadily increased. The developing animals were examined histologically to determine what morphological changes correlated to the molecular changes we observed. During metamorphosis the glochidial tissues are degraded and the animals develop the juvenile morphology. Following metamorphosis the juveniles possess a foot, two adductor muscles, a stomach, gastric shield, crystalline style, and gill bars. This study provides a detailed description of the timing and development of these features and is the first attempt to use both molecular and morphological characters to describe the process of metamorphosis in unionid mussels.
The Systematics of Planktomya, a Bivalve Genus with Teleplanic Larval Dispersal

Serge Gofas

Departamento de Biologia animal, Facultad de Ciencias, Universidad de Málaga, E-29071 Málaga, Spain. E-mail: sgo@uma.es

The small bivalve Planktomya henseni Simroth, 1896 (type species of Planktomya Simroth, 1896), originally described as a pelagic species from a plankton tow in the North Atlantic and later recognized as a benthic Caribbean species, is shown to be also present in the Eastern Atlantic, in the islands off West Africa. The morphology of adults and protoconchs is redescribed and figured taking into account new material. The Eastern Atlantic species Nesis prima Locard, 1899 (type species of Nesis Locard, (1899), is assigned to Planktomya on the basis of larval shell morphology. The generic name Planktomya has precedence over Nesis (preoccupied), so that the replacement name Monterosatus Beu, 1971 is not necessary. Planktomya prima was described from the continental shelf of Bay of Biscay, and is shown to occur south to Senegal and Guinea. A further species of Planktomya is described from Southern Angola. The systematic position of Planktomya is discussed. It is concluded, on the basis of shared character states of the hinge, ligament and pallial line, that it should be placed in the Montacutidae, in the vicinity of Tellimya Brown, 1827. The current placement of Monterosatus in the Mesodesmatidae is rebutted. The strategy of larval dispersal, with teleplanic larvae, is briefly discussed and noted to be an extreme case of r-strategy, where large quantities of larvae never reach the shelf to metamorphose.
Testing Models of the Relationships of the Extant Anomalodesmatans

Elizabeth Harper(1), Elizabeth Hide(2) and Brian Morton(3)

(1) Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ, U.K.
E-mail: emh@cus.cam.ac.uk
(2) National Museums of Scotland, Chambers Street, Edinburgh EH8 9EJ, U.K.
(3) The Swire Institute of Marine Science and Department of Ecology and Biodiversity, The University of Hong Kong, Hong Kong

The Anomalodesmata are a fascinating bivalve sub-class, with a long evolutionary history dating back 500 million years. Nearly 15% of all the bivalve families that have ever lived are classified within the Anomalodesmata and yet the relationships between its constituent taxa (both living and fossil families) remain obscure. The 13 families of extant anomalodesmatans form an extremely diverse group whose members account for some of the rarest and most specialised of Recent bivalves. They exploit a wide range of habitats from shallow to deep sea, as shallow and deep burrowers in soft sediments, or attached to hard surfaces either by byssal threads or by permanent cementation. They include the remarkable “septibranchs” which are voracious predators in the deep-sea and also the enigmatic tube-dwelling clavagellids. This plethora of life habits has led to an equal variety of overall morphologies which has confounded analyses of their phylogenetic inter-relationships based on single character systems and these problems appear to have been further exacerbated by convergent and parallel evolution. In order to overcome these obstacles we have used an approach which takes into account the results of a cladistic study (based on both hard-part and tissue characters) and an analysis of the fossil record.

Phylogeny and Taxonomy of Cementing Triassic Bivalve Families (Prospondylidae, Dimyidae and Ostreidae)
Michael Hautmann

Institute for Palaeontology, University of Würzburg, Pleicherwall 1, 97070 Würzburg, Germany. E-mail: haut@mail.uni-wuerzburg.de

Cementing bivalves belonging to the families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae are an important constituent of Upper Triassic shallow marine ecosystems. Based on new material from the Upper Triassic Nayband Formation of east-central Iran and on type-material from the Alpine Triassic, the taxonomy and phylogeny of these families is examined. The Plicatulidae developed from an ancestor within the Prospondylidae by forming strong crurae, which allowed a reduction of the lateral part of the ligament. Their hinge was later modified by shifting resilifer and crurae in a ventral direction and by forming a secondary ligament dorsally. Only slight modifications of the shell led to the Spondylidae, which are the (post-Triassic) adelphotaxon of the Plicatulidae. For the monophylum consisting of these three families, the name Spondyloidea Gray, 1826 is available. Contrary to some recently proposed classifications, a direct relationship to the morphologically similar Dimyidae and Ostreidae is unlikely.
Comparative Sperm Ultrastructure in Pteriomorphian Bivalves with Special Reference to Phylogenetic and Taxonomic Implications

John M. Healy and Jennifer L. Keys

Department of Zoology and Entomology, University of Queensland, Brisbane,
Australia, 4072. E-mail: jhe@zoology.uq.edu.au jke@zoology.uq.edu.au

Comparative sperm ultrastructure reveals that the Pteriomorphia exhibit the widest diversity of acrosomal morphology to be seen in any bivalve subclass. Pteriomorphian spermatozoa, like those of most other bivalves, are of the classic aquasperm type (conical acrosomal vesicle, short to rod-shaped nucleus, short midpiece composed of two centrioles and a ring of spherical mitochondria, simple flagellum). Whereas most other bivalve subclasses show at least some defining acrosomal feature(s), this does not appear to be the case within the Pteriomorphia. This raises the question as to whether the Pteriomorphia are truly monophyletic or simply more experimental in relation to their sperm morphology. Pteriomorphian superfamilies not only differ substantially from each other in sperm morphology but also show varying levels of diversity between and within families and genera. In the Ostreoidea the spermatozoa are remarkably uniform in their structure, with the exception of the apical region of the acrosomal vesicle which shows potentially useful generic-level variation in the Ostreidae. A very close relationship between the Pectinidae and Spondylidae of the Pectinoidea is demonstrated, with more distant connections to the Ostreoidea, Anomioidea and Limoidea. Within the Mytilidae (Mytiloidea) there is substantial variation between supraspecific taxa especially at the subfamial level.
Dissecting the Latitudinal Diversity Gradient in Marine Bivalves

David Jablonski(1), Kaustuv Roy(2) and James W. Valentine(3)

(1) Dept. Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago,
IL 60637, U.S.A. E-mail: djab@midway.uchicago.edu
(2) Dept. Biology, University of California, San Diego, CA 92093-0116, U.S.A.
(3) Dept. Integrative Biology, University of California, Berkeley, CA 94720, U.S.A.

The latitudinal diversity gradient, with maximum taxonomic richness in the tropics, is one of the most pervasive biological patterns, but its basic configuration and its temporal dynamics remain poorly known for marine organisms. An analysis of 945 bivalve species from the Eastern Pacific continental shelf (northwest Peru to the north coast of Alaska in the Arctic Ocean) confirms the existence of a latitudinal gradient in taxonomic diversity. This gradient is strong in both infaunal and epifaunal bivalves (albeit with different slopes), contrary to Thorson’s (1952, 1957) long-standing hypothesis that only epifaunal groups increase in diversity towards the tropics. Protobranch bivalves do not show a latitudinal trend, and this may reflect the feeding habits of the adults or of the larvae. Given the latitudinal patterns in species richness, and the near-complete turnover of species from poles to equator, it is striking that the size-frequency distribution of species at the provincial level does not change with latitude. As with gastropods in both the Eastern Pacific and western Atlantic, the overall bivalve diversity gradient is significantly correlated with sea surface temperature, even when the effects of latitude are factored out. This supports the hypothesis that biological diversity gradients depend heavily on the total or average energy input, which would be a complex function of solar input (both mean and variance) and productivity. Preliminary data suggest that the species (and genus) extinction and origination rates are higher in the tropics than in the Arctic, but the modal body sizes of bivalve faunas have not been evolutionary attractors.
Palaeoenvironmental Reconstruction from Ontogenetic Records in the Shell of the Queen Scallop, Aequipecten opercularis (L.)

Andrew L.A. Johnson(1), J.A. Hickson(1), J. Swan(1), M. Brown (1), T.H.E. Heaton(2), P.S. Balson(2) and S. Chenery (2)

(1) Department of Earth Sciences, University of Derby, Derby DE22 1GB, U.K. E-mail: A.L.@derby.ac.uk
(2) British Geological Survey, Keyworth, Nottinghamshire, U.K.

Aequipecten opercularis is a widespread scallop, occurring at present from northern Norway to the Adriatic, and extends back to the Miocene. Studies on animals cultured under monitored, semi-natural conditions show that the the oxygen of shell carbonate is incorporated in isotopic equilibrium with ambient seawater (hence preserving a record of temperature variation) and that at least in the first year growth is rapid and only interrupted for brief intervals during winter (hence providing for reconstruction of almost the full seasonal temperature range). Seasonal variation is evident in shell magnesium concentration and microgrowth-increment width so there is scope for independent verification of at least the temporal basis of isotopically-determined temperature changes. ‘Summer’ ?O18 values from sub-fossil shells of the North Sea Basin are closely comparable to those from modern shells but ‘winter’ values are somewhat enriched, suggesting either cooler temperatures or (more probably) enhanced food supply/ability to feed, resulting in more continuous winter growth and registration of the very lowest temperatures experienced. Microgrowth-increment data support palaeobiogeographic evidence that Pliocene marine temperatures were substantially higher than at present, but isotopic evidence is contradictory. At the very least this argues for multiproxy investigations of palaeotemperature, and may indicate that factors other than temperature (e.g. food supply) are important in determining the latitudinal ranges of taxa.

Contrasting Structure and Morphogenesis of Ligaments in Cryptodonta and Early Pteriomorphia (Mollusca; Bivalvia)

Paul A. Johnston (1) and Christopher J. Collom (2)

(1) Royal Tyrrell Museum of Palaeontology, P.O. Box 7500, Drumheller, Alberta, T0J 0Y0, Canada. E-mail: pjoh@mcd.gov.ab.ca
(2) Department of Earth Sciences, Mt. Royal College, 4825 Richard Road, Calgary, Alberta, T3E 6K6, Canada

The bivalve subclass Cryptodonta is characterized primitively by an opisthodetic monovincular ligament area with horizontal growth lines and a ventrally accreting, linear, growing margin, but without differentiated zones for insertion of lamellar and fibrous ligament components. Improbably homogeneous, monovincular ligaments may instead have been constructed as in Nucula, with a medial wall of lamellar ligament separated from the hinge plate on either side by a layer of fibrous ligament (granular in Nucula). But unlike Nucula, dorsal placement of the ligament in cryptodonts indicates a predominantly tensile function. Some primitive pteriomorphs such as Cyrtodonta show horizontally striated ligament areas that mimic monovincular ligaments; however, the striations are grooves and ridges, not growth lines, as those ventralmost do not extend the length of the ligament area. These ligaments are duplivincular and differ fundamentally from monovincular ligaments both morphogenetically and functionally. Orientation of grooves on duplivincular ligament areas, whether inclined or subhorizontal, is a simply a vector determined by the rate of propagation of secretory waves along the mantle isthmus and the rate of accretion of the ventral margin of the ligament area. We can now document well-preserved monovincular ligament areas in cryptodonts representing every geologic period from Upper Ordovician “Vlasta” americana to Upper Cretaceous Tenuipteria. Such continuity of monovincular ligament construction through time is important for our phylogenetic arguments that link exclusively Mesozoic cryptodont groups such as Buchiidae, Pergamidiidae, and Halobiidae with older Paleozoic praecardioid cryptodonts, rather than with the Pteriomorphia. An apparent monovincular ligament in the earliest known bivalve Pojetaia (Tommotian) raises the interesting possibility that these ligaments are primitive for the Bivalvia.
Ontogenetic Age Determination and Evolutionary Patterns in Gryphaea from the British Jurassic

Douglas S. Jones

Florida Museum of Natural History, University of Florida, Gainesville, FL 32611,
U.S.A. E-mail: dsjo@flmnh.ufl.edu

Few bivalves have played a more significant role in evolutionary studies than the coiled Jurassic oyster, Gryphaea. Since the seminal work of Trueman (1922), we have known that the Lower Jurassic Gryphaea lineage of Britain is characterized by phyletic size increase and heterochronic change in shape. Subsequent work by Hallam indicated that this increasing size was accompanied by an overall juvenilization of form. The evolution of shape represents a clear case of paedomorphosis. However, without the ability to standardize samples by common age or stage of development, it remained impossible to specify the mode of heterochrony responsible for this paedomorphic result. Johnson’s (1993, 1994) reanalyses of evolutionary patterns in this lineage identified the same procedural problem discussed earlier by Gould (1972) and found to be at the heart of the coiling debate – improper standardization when comparing ancestors and descendants. Fortunately, annual growth increments revealed in shell cross-sections permit ontogenetic age and growth rate determinations for sample populations throughout the lineage. Growth curves indicate that phyletic size increase in Liassic Gryphaea is achieved by faster growth and not by a hypermorphic extension of time to maturity. The well-known decrease of coiling in the upper part of the sequence, accompanied by increasing size and juvenilization of form, represents a true case of neoteny (Jones and Gould, 1999). An independent series of Gryphaea from the Middle-Upper Jurassic reveals a strikingly different pattern. Direct measurement of ontogenetic age using periodic growth increments provides a powerful mechanism to assess heterochronic style in evolving bivalve lineages.
Giant Bivalves from a Barremian (Early Cretaceous) Seep System in Wollaston Forland, Northeast Greenland

Simon R.A. Kelly, Eric Blanc, Simon P. Price and Andrew G. Whitham

Cambridge Arctic Shelf Programme, Gravel Hill, Huntingdon Road, Cambridge CB3 ODJ, U.K.

Anomalous mound-forming limestones, here termed the Kuhnpasset Beds, occur within Barremian mudstones from Wollaston Forland. They contain a locally abundant and unusual faunal assemblage, dominated by bivalves. The taxa include a giant permophorid gen. et sp. nov., reaching 300 mm length, lucinaceans including Cryptolucina, Solemya sp. and drift-wood with the wood-boring Turnus sp. The form of the mounds with calcite cemented tube systems, associated calcite crusts and laminated void fills probably indicates a cold-seep complex. Although shell preservation is siliceous, which precludes geochemical studies concerning their origin, it is probable that the seeps are methane-related. It is believed that the mounds formed on a mid- to outer shelf situation during the period of quiescence following earlier Cretaceous extensional rifting on the eastern Greenland passive Atlantic margin. The underlying faults may have contributed to hydrocarbon reservoir formation. Seepage along faults through the seals of the reservoirs was active during Barremian but had ceased by Aptian time.
Relevance of Sperm Ultrastructure to the Classification of Giant Clams (Mollusca, Cardiodea, Cardiidae, Tridacninae)

Jennifer L. Keys and John M. Healy

Department of Zoology and Entomology, The University of Queensland, Brisbane, Australia, 4072. E-mail: jke@zoology.uq.edu.au; jhe@zoology.uq.edu.au

Sperm ultrastructure of six out of eight of the living species of giant clams (traditionally regarded as a distinct family Tridacnidae, superfamily Tridacnoidea) is examined and the data discussed firstly in relation to other bivalve sperm and secondly in relation to recent taxonomic and phylogenetic studies on the Cardioidea. The results support the work of Schneider (1992, 1995, 1998a,b) that the Tridacnidae should be regarded as a subfamily of the Cardiidae (as Tridacninae), and are not worthy of being placed in a separate superfamily.

Tridacnine spermatozoa are all of the aquasperm type, featuring, in anterior-posterior sequence: a conical acrosomal vesicle, an oblong to rod-shaped nucleus, a short midpiece region (with a proximal and distal centriole surrounded by a cluster of four, round mitochondria) and a flagellum (axoneme of 9+2 microtubular pattern). Although the midpiece of most species follows essentially the same pattern throughout the group (a pattern seen throughout the Bivalvia), there are substantial differences between species in the shape, length and volume of the nucleus, and in the spatial relationship between the acrosomal complex and the nuclear apex. Results of our study clearly show a dichotomy within the Tridacninae between Tridacna (subgenera Tridacna sensu stricto, Persikima, Chametrachea) on the one hand and Hippopus on the other. This is based on the occurrence in the Tridacna of a prominent nuclear peg which fits into the invaginated base of the acrosomal vesicle (peg absent in Hippopus) and the presence in Hippopus of a well developed centriolar rootlet, lying lateral to but contacting the centrioles (rootlet vestigial or absent in Tridacna). Given the occurrence of a apical protrusion of the nucleus in several investigated Cardiinae, either as a discrete peg as in Cerastoderma, or a broad bump as in Lunulicardia, the complete absence of a protrusion in Hippopus is presumably due either to secondary loss or perhaps even diphyly of the Tridacninae. Within Tridacna, the species T. (Chametrachea) maxima and T. (C.) crocea are distinguished from other species of the genus by a strongly attenuate nucleus and a considerably smaller acrosome. In contrast, and against expectation, T. (C.) squamosa shows acrosomal and nuclear dimensions very close to that obtained for T. (Tridacna) gigas.
Ecological Fidelity of Molluscan Death Assemblages

Susan M. Kidwell

Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, U.S.A. E-mail: skid@midway.uchicago.edu

Although individual studies have yielded mixed results, a comparative analysis of marine molluscan faunas and their associated dead from 17 study areas) indicates that sedimentary death assemblages are very robust reflections of local community composition. Virtually all live species (mean 89% ± 5) are present in the local death assemblage, dead individuals overwhelmingly belong to species found living in the same habitat (mean 82% ± 10), and the rank abundances of dead species do not diverge significantly from those of live species (80% of datasets tested; p < 0.05). Even small samples of the death assemblage thus capture basic dominance information and habitat preferences of the live fauna, with only slight differences in fidelity among environments (marshes and tidal creeks; intertidal flats; coastal embayments; open marine seafloors). This correspondence is especially striking given the number of post-mortem processes that might act to bias such a record. Because the species richness of a death assemblage is typically 2-3x greater than that of any single census of the local live community, inverse metrics such as “% dead species also present alive” suggest low live-dead agreement. However, the majority of dead-only species are rare and most of the discrepancy (excess dead species richness) is evidently due to under-sampling of the live fauna. When limits imposed by sampling are considered, true post-mortem bias from the addition of exotic and relict shells is probably less than 25% of total dead species richness, and would have little effect on abundance-based diversity measures. In general, because of their greater numerical abundance, bivalve species are less affected than gastropod species. Molluscan death assemblages thus provide a reliable-plus relatively rapid and inexpensive-means of assessing community composition, both for the purpose of establishing ecological baselines as well as for paleoecological analysis of ancient rocks. Continuing work focuses on the types of species (body sizes, shell mineralogies or microstructures, life habits, habitat types) that are correlated with under- or over-representation in the sedimentary record, and in acquiring datasets from low latitudes and from areas with long-term replicate sampling of live faunas.

Pectinid Bivalve Pedum and the Amount of Surface Occupied in Host Corals (Red Sea)

Karl Kleemann

Institute of Palaeontology, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria
E-mail:Karl@univie.ac.at

The pectinid boring bivalve, Pedum spondyloideum (Gmelin 1791), associated to scleractian hosts, lives embedded in the coral skeleton, usually completely surrounded by live tissue (Kleemann 1990). In the northern Red Sea, off the ports of Hurgada and Safaga, and at Zabargad Island, close to the Sudan, associations of Pedum with coral hosts were observed in the field. Documentation took place by in situ colour slides. Two frame sizes,
9 x 6 cm and 19 x 13 cm respectively, were used on a Nikonos II camera with electronic flash. A small collection was used for measurements of the shells and their dwellings. The size-relation between shell and dwelling is very good. The relation between dwelling length and dwelling volume was used to determine a formula to estimate the occupied volume in the hosts from the photographs. The selection of photographs was taken under the aim (1) to document the range of host corals in generic and specific level as far as possible, and (2) to record high densities of the bivalve in certain hosts. The associations with corals Hydnophora microconos, Pavona cactus and P. varians are here recorded for the first time.
Live coral surface versus occupied coral surface (OCS) was measured in the scanned pictures, format DIN A4, by Autocad program. For easy comparison between coral hosts, values were converted to 100 cm2 coral surface. They are not convertible to larger scale, as maximum densities usually apply only to parts of the host colony, and “mean” values are derived from the available sub-samples. On various coral carpets, Pedum density ranged from 0 to 17.8 individuals m-2 (Zuschin & Piller 1997). In the 9×6 cm frames, 1.9 to 18.6 Pedum occurred per 100 cm-2. The maximum was found in a Montipora, with 12.45 % OCS. Mean density in Montipora (n = 11) was 7 100 cm-2, and the mean OCS amounted 3.8 %. In the 19×13 cm frames, density ranged from 0.4 to 10.7 Pedum 100 cm-2. The maximum occurred again in Montipora, followed by Porites (6.7 100 cm-2) and Cyphastrea (5 100 cm-2). The OCS ranged from 0.18 to 7.04 %. The latter was found in Goniastrea, and amounted up to 6.63 % in Montipora. Mean density in Montipora (n = 12) was 3.7 Pedum/ 100 cm-2, mean OCS 2.12 %. From the known dwelling length, the expected volume is found using the potential regression y = 0.2127 x 2.7447. A high Pedum density indicates a rather near-shore locality with ample suspended nutrients in the water passing by. No indication was found that hosts would suffer seriously from heavy infestation. Corals usually outlive their inhabitants by many years, which is demonstrated by successions of Pedum generations in the same host. The traces, embedded in the skeleton, are not so distinct as in coral associated mytilid Lithophaga (Kleemann 1994). Due to the in comparison to the latter less regular shape of Pedum dwellings and their much wider openings, coral overgrowth results in partly filled and camouflaged dwellings. Nevertheless, they have the potential to yield trace fossils.
Bivalve Habitat Expansion of Shoreface Bivalves: A Reconstruction based on the Mesozoic and Cenozoic of Japan

Yasuo Kondo, Koji Hirose, Kazuhiro Sugawara, Naoki Kikuchi, Nobutaka Funayama and Tomoki Hiraoka

Department of Geology, Kochi University, Kochi 780-8520, Japan.
E-mail: ykondo-u.ac.jp

Habitats of fossil bivalves were reconstructed for more than 50 fossiliferous shoreface sediments spanning from Triassic to Holocene and Recent in Japan, based on sedimentary facies, taphonomical and palaeoecological observations along with examination of published information. The results well outlined long-term history of bivalve habitat expansion to shoreface environment and evolutionary replacement within this environment. Trigoniids were the chief inhabitants of shoreface in the Mesozoic time. For example, lower shoreface environments were inhabited by a trigoniid, Vaugonia, in the earliest Jurassic. Nipponitrigonia was probably the first bivalve, which appeared in abundance from upper shoreface sediments, and this occurred in the Late Jurassic or early Cretaceous. Also venerids and glycymeridids occurred in the lower shoreface, but they but did not expand their habitats to the upper shoreface at this time. Members of the Veneridae and Mactridae successfully established their habitats in the upper shoreface sometime between Late Cretaceous and Miocene. Particularly mactrids became abundant in the Miocene of north Japan, along with other bivalves with various modes of life, including members of the Cardiidae, Tellinidae, Solenidae and Hiatellidae. The reconstructed colonization history suggests that bivalves expanded their habitats to increasingly more physically unstable, high-energy environments by developing adaptive features, such as (1) large and thick shell (Trigoniidae), (2) streamlined shell form (Veneridae), (3) light-weight shell (Mactridae).
Significance of Gill Characters for Taxonomy in Sphaeriidae (Eulamellibranchiata) and Some Other Bivalve Groups

Alexei V. Korniushin

Institute of Zoology, B.Khmelnitsky str.15, 252601-Kiev, Ukraine
Present address: Museum fuer Naturkunde, Invalidenstr. 43, D-10115 Berlin, Germany

Freshwater bivalves of the family Sphaeriidae traditionally arranged in three genera are characterized by a certain reduction of ctenidia. Degree of this reduction varies between genera. In contrast to Sphaerium and Musculium, the outer demibranch of Pisidium (except Pisidium idahoense Roper and P. subtilestriatum Lindholm) consists of the one lamella only. Specific differences in size and position of the outer demibranch were noticed within the latter genus by earlier investigators. In this study, position of the outer demibranch was quantified by marking the inner demibranch filament number corresponding to its anterior edge. The obtained figures were treated statistically and differences between species and/or species groups were confirmed. Some patterns of ctenidium ontogenesis were also studied in different sphaeriid taxa. It was shown that position of the outer demibranch usually does not change in ontogenesis; the time of the outer demibranch appearance and its growth rate significantly varied between species and genera and might be treated as taxonomic characters as well. Correlation between the time of appearance and topographic position of the organ was observed. Noticeable differences in the outer demibranch position and growth rates were also reported for Cerastoderma and Hypanis (Cardioidea) and for Corbicula and Neocorbicula (Corbiculidae). Only the growth rates differed in Unio and Anodonta (Unionidae). One-lamellar ontogenetic stage similar in structure to the gill of Pisidium was observed in Sphaerium, as well as in corbiculids, cardiids and Mya. Other modes of the outer development were observed in mytilids, unionids, dreissenids and scrobiculariids. It was concluded from comparison of these modes, that namely the descending lamella is reduced in the outer demibranch of sphaeriids. The characters observed here were already applied in phylogenetic analysis and taxonomy of Pisidium (on species level). Their applications for the taxonomy of Unionidae, Corbiculidae and Cardiidae on generic level seem to be also rewarding.
Physical Constraints in Scallop Swimming: Take-Off and Swimming Mechanics

Michael LaBarbera

Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, U.S.A. E-mail: mlab@midway.uchicago.edu

Take-off from the substrate and swimming were recorded for the scallops Chlamys hastata (N = 10), Chlamys rubida (N = 22), and Crassodoma gigantea (N = 7) using high-speed (125-250 frames/sec) video. The two Chlamys species swim throughout their lives, but Crassodoma swims only as juveniles; adults are cemented to the substrate. Video recordings were analyzed to determine clap frequency, instantaneous accelerations, and average speed. Scallops ranged in height from 5-65 mm for the Chlamys species and 26-45 mm for C. gigantea. Peak acceleration for all three species was approximately 0.5 ms-2; the largest and smallest individuals exhibited lower accelerations than intermediate-sized animals. Average swimming speed (integrated along the animal’s path) for the three species ranged from 10-40 cm/s. Larger animals achieved higher absolute swimming speeds, but relative speeds (shell heights/sec) were maximal in the smallest animals and declined linearly with increasing shell size. For all three species, clap frequency was a linear function of shell height; C. gigantea was indistinguishable from the two Chlamys species during its byssally-attached phase. Using published data for an additional seven species of scallops, a single function describes the relationship between shell height and clap frequency for all scallops, independent of phylogenetic relationships or environmental temperature. These data are the first measurements of acceleration during jetting for any scallop and the first quantitative description of swimming in juvenile Crassodoma.
Hydrodynamics of Fossil Hippuritids: A Novel Feeding Strategy in an Asiphonate

Michael LaBarbera(1) and Eulàlia Gili(2)

(1) Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th St., Chicago, IL 60637, U.S.A. E-mail: mlab@midway.uchicago.edu
(2) Dept. de Geologia, Univ. Autònoma de Barcelona, Edifici C, 08193 Bellaterra
(Barcelona), Spain

Hippuritid rudists inhabited Cretaceous shallow carbonate platforms, living partially embedded in the sediment in dense aggregations. Differential growth of the right valve elevated the commissure above the sediment-water interface. The operculiform left valve bore a system of radial canals which communicated with the water through pores believed to represent incurrent regions. Hippuritids often preserve inclined 30-45° off vertical, an orientation that appears primary and the result of active growth processes. Laboratory flume experiments revealed that cylinders tilted downstream generate an intense vortex that lifts water off the substrate to bathe the cap (equivalent to the hippuritid left valve). Paired model hippuritids were deployed in the Mediterranean Sea in various orientations and configurations; water was drawn through the models and a 2 µm filter in series. Filters were dried, weighed, and ashed to determine organics captured. Vertical and upstream-tilted models in unidirectional flow caught similar quantities of organics; downstream-tilted models caught significantly more than both. In oscillating flows, inclined models, either solitary or in aggregations, captured more organics than vertical models. Models in aggregations caught more organics than solitary models; models on the edge of aggregations captured more than those in the center. Similar experiments on a modern carbonate platform (San Salvador, Bahamas) produced identical results. An inclined orientation permitted hippuritids to exploit resources unavailable to vertically-oriented rudists.

This paper will be presented as part of the Feeding Workshop.
Connecting Bivalve Functional Morphology to Ecosystem Processes

Jeffrey S. Levinton (1), J. Evan Ward (2), Shirley M. Baker (1) and Sandra E. Shumway (3)

(1) State University of New York at Stony Brook, Stony Brook, NY 11790, US..A.
E-mail: levi@life.bio.sunysb.edu
(2) University of Connecticut
(3) Southampton College, Long Island University

Bivalves respond to changes in food quality, principally by means of altering clearance rates and by selective ingestion. We employ a video endoscopy to examine the movement of particles in the pallial cavity and aid in sampling particles with a micropipet, which are analyzed with a flow cytometer. We can distinguish among phytoplankton species and non-living particles. Particle selectivity is the rule for several bivalve species, with at least two cases of rapid particle selection on the gills. As might be expected, living phytoplankton are generally favoured over cellulose-dominated detrital particles and seaweed detritus. Bivalves also select among phytoplankton. These selectivities are generally correlated with clearance rates, which are higher for particles that are selected. This research is taking two directions. From an evolutionary perspective, it would be useful to connect the evolution of gills with changes in selectivity, but we are encountering new mechanisms of selectivity with nearly every new gill architecture we examine, so much more information is required to meet this objective. On the other hand, selectivity can be related to ecosystem function, as bivalves often exert strong controls on the phytoplankton in estuaries. Our studies in this area show that bivalves can exert profound impacts on the plankton and other benthos. In the Hudson River estuary, zebra mussel particle selectivity can account for the decline of a dominant part of the phytoplankton. High zebra mussel pumping rates combined with strong resource overlap in selectivity explains the decline of native unionid mussels with similar selectivity but the relative insensitivity of another unionid, owing to its lack of selectivity for particles.
Extinction and Infaunality: Taxonomic and Morphological Patterns in Veneroid Bivalves from the Paleogene of North America

Rowan Lockwood

Committee on Evolutionary Biology, University of Chicago, 1025 E. 57th Street, Chicago, IL 60637, U.S.A. E-mail: r-lo@uchicago.edu

Although the causes of mass extinctions have been studied in detail, the long-term effects of extinction on the evolutionary trajectories of clades are poorly understood. The early Cenozoic history of veneroid bivalves represents an ideal system in which to investigate the possible relationship between mass extinctions and long-term evolutionary change. This study explores taxonomic and morphological trends within a veneroid clade and focuses primarily on extinction patterns associated with the Paleocene-Eocene and Eocene-Oligocene transitions in North America. Questions addressed include: (1) Do taxonomic and morphological patterns of extinction differ in magnitude, rate, or duration? (2) Are patterns of extinction selectivity and preferential recovery evident in morphospace? (3) How do these patterns of selectivity correspond to long-term morphological and ecological trends in this clade? I explore these questions by constructing an empirical morphospace based on shell outline and pallial line data for over 100 Paleogene subgenera of veneroids, arcticoids, and glossoids from North America. Patterns are summarized via eigenshape analysis, using points distributed around the shell circumference and the pallial line. Extinction selectivity and preferential recovery are assessed by comparing the distributions of taxa in morphospace and levels of morphological diversity among time intervals. The close correlation between shell morphology and burrowing behavior in these bivalves also allows me to examine trends in ecological and functional morphological traits. Preliminary results indicate that preferential survivorship of deeply burrowing taxa across both the Paleocene-Eocene and Eocene-Oligocene transitions corresponds closely with ecological trends towards increasing infaunality throughout the Paleogene in this clade. These results contrast markedly with the elevated levels of extinction observed in deeply burrowing veneroids at the K-T boundary.
Colonization of Bivalves at Nascent Hydrothermal Vents along the East Pacific Rise

Richard A. Lutz(1), Timothy M. Shank(1) and Daniel J. Fornari(2)

(1) Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, U.S.A.
(2) Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A.

In April, 1991 a volcanic eruption along the crest of East Pacific Rise (EPR) between 9º45 ‘N and 9º52’ N initiated the formation of numerous hydrothermal vents. This catastrophic event provided a unique opportunity to follow successional patterns of biological community development from the birth of a series of selected deep-sea hydrothermal
vents within the axial summit trough of the EPR between 9° 49.88’N and 9º50.10’N at a depth of approximately 2510 m. These nascent ecosystems were subsequently visited and imaged extensively using a variety of photo- and videographic systems mounted on the deep-diving submersible Alvin during cruises in: March, 1992; December, 1993; October, 1994; November, 1995; November, 1997; and May, 1999. By December, 1993, the vents were extensively colonized by numerous vent-endemic organisms, including vestimentiferan tube worms (Riftia pachyptila and Tevnia jerichonana), zooarcid fish, alvinellid polychaetes, amphipods, colonial siphonophores (dandelions), copepods, octopods, limpets, and galatheid and brachyuran crabs. Mussels (Bathymodiolus thermophilus) and clams (Calyptogena magnifica), which are common members of many hydrothermal vents visited to date along both the EPR and the Galapagos Rift, were not seen in any of the images taken in December, 1993. In October, 1994, a few small mussels
(2 – 10 cm shell length, at maximum densities of five individuals per square meter) were observed on basaltic substrates within 0.5 – 6 m of a number of the vestimentiferan-dominated communities; no mussels were observed amongst or attached to any of the vestimentiferan tubes. By November, 1995, the number and density of mussels at specific sites had increased, with mussels (maximum shell length = 12 cm) forming occasional tight
clumps (with 4 – 12 individuals per clump). For the first time, mussels (less than 12 individuals) were observed to be attached to vestimentiferan tubes. Despite extensive imaging utilizing a high-resolution, macro video camera, no vesicomyid clams (Calyptogena magnifica) were observed during the 14 Alvin dives to the region in 1995. By November, 1997, the mussel populations continued to increase in density and aerial extent, and vesicomyid clams (a total of 7 individuals) with maximum shell lengths of 8 cm, were first observed in the region. By May, 1999, approximately 50 vesicomyid clams (maximum shell lengths = 10 – 11 cm) were seen in basaltic cracks and crevices in the area, with up to 15 clams occupying a single meter-long crack. Extensive mussel beds now dominate the majority of vent communities along this portion of the ridge crest, with hundreds of thousands of mussels inhabiting a region in which no mussels had been seen five years earlier.

Prodigious Polyphyly in Imperiled Freshwater Pearly-mussels (Bivalvia: Unionidae): An examination of Species and Generic Designations
Charles Lydeard(1), Russell L. Minton(1), and James D. Williams(2)
(1) University of Alabama, Biodiversity and Systematics, University of Alabama, Box 870345, Tuscaloosa, Alabama 354871, U.S.A. E-mail: clyd@biology.as.ua.edu
(2)U.S. Geological Survey, Biological Resources Division, 7920 NW 71st Street, Gainesville, FL 326532, U.S.A.
Unionid bivalves or freshwater pearly-mussels (Unionacea: Unionidae) serve as an exemplary system for many of the problems facing systematists and conservation biologists today. Most of the species and genera were described in the late 1800s and early 1900s, but few phylogenetic studies have been conducted to test conventional views of classification. The pearly-mussels of the Gulf Coastal drainages of the southeastern United States from the Escambia (southern Alabama to Florida) to the Suwannee Rivers (Florida) are an unique fauna comprised of approximately 100 species of which about 30 are endemic to the region. In this study, we used mitochondrial cytochrome c oxidase and 16S rRNA gene sequences to test the monophyly and estimate the evolutionary relationships of five unionid species representing three different genera. The molecular phylogenies depict all three genera as polyphyletic. The prodigious polyphyly exhibited within unionids is due to incorrect notions of homology and false assumptions about missing anatomical data. In contrast, the molecular phylogeny provides evidence to support the recognition of all five unionid species as distinct evolutionary entities. Furthermore, evidence supports the elevation of Quincuncina infucata of the Suwannee River as a genealogical species.

Mismatching Resilience with Human Exploitation: Population Structure of the Brown Mussel, Perna perna, in South Africa

Christopher McQuaid

Department of Zoology & Entomology, Rhodes University, Grahamstown 6139, South Africa

The intertidal mussel Perna perna is intensively exploited for food on the south and east coasts of South Africa. Rates of inshore primary production decrease from west to east along the coast, coinciding with increasing density of coastal human populations. As a result, non-commercial, subsistence level exploitation is most intense where the ability of mussel populations to sustain such exploitation is likely to be lowest. Several population parameters are influenced by degree of wave exposure, but the effects depend on height up the shore. Densities of plantigrad settlers decrease upshore. Settler densities are also higher on exposed sites, though only on the low shore. Growth is twice as fast on exposed shores as on sheltered shores. Although mortality rates are also higher on exposed shores, they support larger mussels. The opposite is true in Britain. As with recruitment, differences between exposed and sheltered shores disappear farther upshore, where other abiotic stresses, associated with emmersion, mask the influence of exposure. These findings indicate that exposed shores are likely to be more resilient to exploitation than sheltered shores because recruitment and growth are more rapid. Ironically, just as the eastern coastline is both more vulnerable and more heavily exploited, so predation pressure by people is likely to be greater on the more vulnerable sheltered shores.
Phylogeny and Character Evolution Inferred from Early Life History Shells of Middle Jurassic and Living Bivalves

Nikolaus Malchus

Freie Universität Berlin, Malteserstr. 74-100, Haus D 12249 Berlin, Germany.
E-mail: nik@cc.uab.es

Four case studies document the value of early life history shells of fossil bivalves (here middle Jurassic) as a tool to infer phylogenetic relations and character evolution: Case 1 demonstrates that larval shells of Juranomia possess a small shell process on the antero-ventral inner commissure of the P II that plugs the byssal notch of the lower right valve. The same features are characteristic of many living anomiids and are supposed to be an autapomorphy of the family’s stem species, therefore. Case 2 presents strong additional support for the monophyly of the Gryphaeidae and Ostreidae based on the presence of the postero-dorsal notch in left valves of middle Jurassic Liostreinae and Gryphaeinae. The character is autapomorphic for the ancestral species. Case 3 provides evidence that the growth direction of the ligament changes at least twice during ontogeny of some multivincular pterioids that are tentatively determined as bakevellids. In addition, the comparison of larval hinge characters of bakevelliids, oysters and mytilids allows to identify the centrally positioned hinge denticles in oysters as representing only the posterior half. Though reduced, the anterior part is still present in modern Gryphaeidae but has been entirely lost in most (perhaps even all) Ostreidae. Case 4 illustrates an example where, ontogenetically, lamellar teeth of the arcoid genus Grammatodon apparently form by subsequent fusion of taxodont teeth. If this observation can be confirmed, lamellar teeth within the Arcoida are likely of two different origins and thus not homologous throughout.
Palaeoenvironmental Analysis by Means of Pectinid Coquinas in the Lower Miocene of Northeastern Egypt

Oleg Mandic (1) and W.E. Piller (2)

(1) Institute of Palaeontology, University of Vienna, Geozentrum, Althanstr. 14, A-1090 Vienna, Austria. E-mail: oleg@univie.ac.at
(2) Institute of Geology and Palaeontology, University of Graz, Heinrichstr. 26, A-8010 Graz, Austria

Rich pectinid accumulations were studied within the uppermost Burdigalian of Gebel Ghara 45 km NW Suez. The 120 m shallow marine section of siliciclastics and limestones is composed of several transgressive, fining upwards sequences. Two sequences of the lower, more siliciclastic part of the section are in particular characterised by the occurrence of five distinct pectinid coquinas. The composition of the coquinas (three of the lower, two of the upper sequence) was defined by counting at least 110 specimens out of each. Five dominating genera were identified: Amussiopecten, Flabellipecten, Macrochlamis, Oppenheimopecten, and Pecten. Besides the dominating Pecten, Amussiopecten and Macrochlamis characterize the lowermost coquina. The occurrence of strongly sculptured Macrochlamis indicates high water energy. The second coquina is dominated by Flabellipecten, followed by Pecten and Amussiopecten; Macrochlamis is replaced by Oppenheimopecten. The shift towards weakly sculptured, thinner and articulated shells indicates lower water energy, however, above storm weather wave base. The uppermost coquina of the lower sequence is totally dominated (99%) by one large Flabellipecten morphotype. Its taphonomic features indicate repetitive destruction of the area by high energy events. Bathymetrically it can be placed around storm weather wave base. Near the base of the second sequence two taxonomically similar coquinas occur both dominated by Oppenheimopecten, with Pecten and a small Flabellipecten morphotype in addition. Thin to medium thick, low ribbed and sculptured shells and frequent articulation indicate lower water energy.
The Evolution of Eyes in the Bivalvia

Brian Morton

The Swire Institute of Marine Science and Department of Ecology and Biodiversity, The University of Hong Kong, Hong Kong, China

Typically, a pair of cephalic eyes located on the axes of the anteriormost filaments of the inner demibranchs of the ctenidia and comprising simple, sensory, pigment cups, occurs in many representatives of the Arcoida and Pteriomorpha. Such eyes also occur in some bivalve larvae and may represent a larval adaptation that is retained into adult life in only some lineages. Ectopic eyes also occur in many representatives of the Arcoida and Pteriomorpha, on the posterior mantle margin, typically the outer fold. These too are generally of simple construction, leading to, in the Arcoida, a pigment cup that is formed into an arthropod-like ‘ommatidium’ eye-spot. Sensory reception is, however, ciliary based and the structure is thus analogous, not homologous, to eyes of superficially similar plan in other phyla. The most complex pallial eyes occur in representatives of the Pectinoidea, with a lens, double retina, argentea and pigment cup, but on the middle mantle fold. Simpler pallial eyes occur in the Cardiidae on the inner fold, but there is still a lens, retina and an argentea. In the Tridacnidae the many hundreds of eyes in the greatly expanded siphons have a similar plan, but the reflecting cup is constituted by zooxanthellae. Eyes as complex as those of the Pectinoidea also occur in the Laternulidae (Anomalodesmata), but on the inner mantle fold. A ciliated, accessory, sense organ accompanies most more advanced bivalve pallial eyes. Pallial eyes are thus of sporadic occurrence in the Bivalvia and their sophistication has not, hitherto, seemed to follow a general plan of progressive development. This is not so, however, and is herein identified. Nevertheless, the question is asked; what is the function of such, in some cases, complex eyes? Virtually all bivalves have an ‘off” shadow reflex which elicits adduction, siphonal retraction or digging. Even those with the most complex eyes, however, do little more when stimulated by a shadow, representatives of the Laternulidae, simply flicking sand grains over the siphonal aperture to camouflage them. Members of the Pectinoidea are thought to be able to detect vicinal movement and theoretically could respond to this by swimming. The pectinid eye can also form a simple image, but is this analysable in the brain, i.e. the optic lobes of the visceral ganglia? The question is posed, therefore; why have such complex eyes evolved?
Evolution of Parental Care and Ovulation Behavior in Oysters

Diarmaid Ó Foighil (1) and Derek J. Taylor (2)

(1) Museum of Zoology and Department of Biology, University of Michigan, Ann Arbor, Michigan 48109-1079, U.S.A. E-mail: diar@umich.edu
(2) Department of Biological Sciences, SUNY at Buffalo, Buffalo, New York 14260, U.S.A. E-mail: djta@acsu.buffalo.edu

Approximately half of all living oysters brood offspring in the inhalant chamber of their mantle cavities; the remainder are broadcast spawners which do not engage in parental care of young. Ostreid ovulation involves a complex behavioral sequence, unique among bivalve molluscs, that results in the countercurrent passage of newly spawned eggs through the gills (ctenidia) and into the inhalant chamber. A trans-ctenidial ovulation pathway is common to both brooding and non-brooding ostreids and, if this behavior represents a brooding adaptation, its distribution is consistent with a secondary loss of parental care in broadcast spawning lineages. We tested this hypothesis by constructing phylogenetic trees based on a 941 nt 28S ribosomal gene fragment, and on a combined molecular/ morphological data set, from representatives of all three ostreid subfamilies together with gryphaeid and non-ostreoidean pterioid outgroups. Our results indicate that: (1) the Ostreidae are robustly monophyletic; (2) broadcast spawning and larval planktotrophy are ancestral ostreid traits; (3) trans-ctenidial ovulation did not evolve as a parental care adaptation; (4) brooding originated once in the common ancestor of the Ostreinae/Lophinae, involved a modification of the final behavioral step in the ancestral ovulation pathway, and has been retained in all descendent lineages. Our data permit an independent test of fossil-based ostreid phylogenetic hypotheses and provide novel insights into oyster evolution and systematics.
Metabolic Rates of Antarctic Stenothermal Bivalve Molluscs

Lloyd S. Peck

British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, U.K.
E-mail: lsp@pcmail.nerc-bas.ac.uk

Antarctic ectotherms have evolved to live in one of the most thermally stable environments on earth. In high Antarctic sites temperatures vary by less than 0.2°C about a mean annual value of -1.8°C. In the maritime Antarctic temperatures range from -1.8°C to + 1.0°C. Bivalves living there have evolved low metabolic rates, and little or compensation for low temperature is seen in metabolism. Here metabolic rates of three species of bivalve mollusc from Antarctica, Laternula elliptica, Cyclocardia astartoides and Limopsis marionensis, were measured at 0°C +/- 0.5°C. All had low rates of oxygen consumption compared to temperate bivalves, and rates were reduced in line with a Q10 of 2, indicating no temperature compensation. Upper lethal temperatures for all three species were between 5°C and 10°C, showing their stenothermal nature. Previously published data indicate oxygen supply to be critical in setting upper limits in these stenothermal species.
Random Walk Evolution in Dunbarella, a Palaeozoic “Paper Pecten”

Christopher Peel

School of Earth Sciences, University of Leeds, Leeds LS2 9JT, U.K. E-mail: CPe@earth.leeds.co.uk

Bivalves are not renowned for displaying rapid evolutionary rates and species duration is often measured in tens of millions of years. The exception to this rule appears to be provided by lineages of thin-shelled, flat-valved “paper pectens” that are often encountered in oxygen-restricted facies of the Palaeozoic and Mesozoic. This study looks at one such example, Dunbarella, from the UK, Europe and North America, through 40 million years of the Carboniferous. Where possible, a zone by zone morphometric analysis records the evolution of the lineage. Using analyses of single character data and principle component studies of those characters it is possible to examine evolutionary trends. Results show that, for a range of analyses, evolution of Dunbarella “jittered” around in a random walk with reversals being commonplace. There is no evidence of stasis or cladogenesis within this lineage. The evolutionary pattern is similar to that recorded by the Builth trilobites of Sheldon (1987).
Shell Scars on Glycymeris glycymeris: Fishing, Predators or Storms?

Kirsten Ramsay, Michel J. Kaiser and Christopher A. Richardson

School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey, LL59 5EY, U.K. E-mail: k.ra@bangor.ac.uk

Scarring in bivalve shells occurs when sub-lethal shell damage is repaired and these scars could potentially be used as indicators of historic disturbance. When viewed in cross-section the scars appear as major breaks in the continuity of the shell edge. This study examined the following possible causes of shell scarring in the long-lived infaunal bivalve Glycymeris glycymeris (dog cockle): (i) physical disturbance by fishing gears, (ii) unsuccessful predator attacks, and (iii) damage sustained whilst reburying in sediment, possibly after storms. G. glycymeris collected from a heavily fished area had significantly higher levels of scarring than those collected from three lightly fished areas. There was also a correlation between yearly frequencies of scarring and yearly fishing effort. This suggests that at least some of the scars resulted from disturbance by fishing gears. Scars were present on c. 44% of shells of G. glycymeris that had been exposed to a crustacean predator (Cancer pagurus) and then given time to repair the damage. These scars were similar to those observed in the fishing effort study. A study of scarring in animals that were experimentally removed from sediment and allowed to rebury was inconclusive, due to poor growth of animals. There were no significant differences in frequency of scarring between the reburying animals and control (undisturbed) animals. The results of these studies suggest that shell scars can be caused both by anthropogenic disturbance (fishing activity) and by natural disturbance (predators). At present, it is not clear whether storm disturbance commonly causes the type of scarring investigated in this study.
Silurian Cycloconchid Bivalves from Wales and the Welsh Borderland: their Systematics and Phylogenetic Position

Viv Ratter

Department of Earth Sciences, Cardiff University, PO Box 914, Cardiff CF1 3YE, U.K.
E-mail: rat@cardiff.ac.uk

Cycloconchid bivalves (order Actinodontoida) are well known from the Ordovician of Laurentia and Avalonia, but are less thoroughly understood from the Silurian period. Recent studies of bivalve faunas from the Silurian of Wales and the Welsh Borderland have
established the presence of two cycloconchid genera within the area, viz. Actinodonta Phillips, 1848 and Diribeodonta gen. nov. (in prep.). It is apparent that the British Silurian cycloconchids are suitable ancestors to the early veneroid families, although their relationships are obscured by a poor fossil record. However, the genera Cycloconcha, Diribeodonta, and to a less extent Actinodonta, display a dental arrangement intermediate between the earliest cycloconchids (e.g. Carminodonta Cope, 1996 and Copidens Pojeta and Gilbert-Tomlinson, 1977) and the Devonian veneroid Eodon, which suggests that the earliest veneroids may have been established by the Lower Silurian. Comparison of the pedal muscle scars and dentition displayed in Cycloconcha and Diribeodonta with Eodon indicates that these characters are homologous; this provides further evidence that the late Ordovician and Silurian cycloconchids were ancestral to the Veneroida.
Mussel Shells as Biochronometers of Environmental Change

Christopher Richardson and Raymond Seed

School of Ocean Sciences, University of Wales-Bangor, Menai Bridge, Anglesey, LL58 5EY, U.K. E-mail: oss@sos.bangor.ac.uk

Mussels are distributed world-wide and their shells contain a record of the environmental conditions to which they have been exposed throughout their life. Tidally induced microgrowth bands in the prismatic layer and annual lines in the inner nacreous layer provide valuable information concerning the spring-neap lunar tidal cycle and seasonal patterns of shell growth. In this paper we describe how these bands and lines have been used to estimate the age and growth of Septifer virgatus and Perumytilus purpuratus from wave-exposed rocky shores in Hong Kong and Chile respectively. Disturbance events such as unusually high air temperatures during prolonged exposure to air result in the deposition of strongly defined bands in Mytilus edulis chilensis from the Falklands, whilst prolonged and short term chlorination in the cooling waters of power stations inhibits growth in Mytilus edulis resulting in the formation of a distinctive banding pattern. Predator attacks and shell damage events result in the temporary and sudden narrowing of growth bands often with the formation of a distinct cleft on the shell surface. Mussels are essentially sedentary and their shells are excellent integrators of chemical contamination in a given area; in some species their great longevity (in some cases >100 years) opens up the possibility for analysing the past chemical environment in which the mussel has been growing. Mytilus trossulus exposed to wood pulp mill effluent on the west coast of British Columbia demonstrated depressed levels of Zinc in their shells compared to control mussels. Modiolus modiolus from a contaminated dump site in the southern North Sea exhibited elevated levels of Lead, Zinc and Copper in their shells between 1968 and 1976 during a prolonged period of dumping compared with control mussels from a non-impacted site. Because of their widespread distribution in coastal and estuarine waters mussel shells are natural in situ biomonitors of environmental change.

Commercial Exploitation of Bivalves

David Roberts

School of Biology and Biochemistry, Queen’s University, Belfast BT9 7BL, U.K.
E-mail: d.ro@Queens-Belfast.ac.uk

Bivalves have been exploited for food, ornamentation and pearls throughout human history. Current exploitation ranges from small-scale harvesting of natural stocks to intensive cultivation and technical manipulation of pteriids for pearls. Commercial exploitation of bivalves for food is dominated globally by epifaunal taxa such as ostreids, mytilids and pectinids; in addition a high diversity of infaunal species, many of which are of major local or regional importance, is exploited. Annual harvests of bivalves for human consumption represent about 5% by weight of the total world harvest of aquatic resources and have an estimated value exceeding US$4 billion at first sale. Declines in commercially important species, as a result of overexploitation and pollution, led to the global movements of bivalves and the development of aquaculture. The harvesting and cultivation of bivalves has environmental consequences which must be overcome to ensure sustainable management of these valuable resources. This presentation considers how our knowledge of bivalves is applied to address this problem and how, in turn, studies of commercial production of bivalves has improved our understanding of bivalve ecology and biology. Specific topics will include life-cycle and settlement strategies, factors affecting growth, mortality and yields; shellfish contamination and the environmental impact of harvesting and cultivation.
Bivalve Plasma Proteins – A Multitude of Proteins of Unknown Function

William E. Robinson

University of Massachusetts Boston, Department of Environmental, Coastal and Ocean Sciences (ECOS), 100 Morrissey Blvd., Boston, MA 02125-3393 U.S.A.
E-mail: wm.r@umb.edu

Little is known about the various proteins found in bivalve blood plasma. Early studies measured total protein levels. Later works characterized lipoproteins and glycoproteins. SDS-PAGE has revealed over 35 protein subunits in the plasma of various marine species, yet few have been identified. These proteins may be classified as (1) immunological; (2) respiratory; or (3) transport/ion regulatory. Immunological proteins (e.g. lysozyme, acid phosphatase) participate in the general immune response and are generally associated with phagocytosis, ìrespiratory burstî or “degranulation”. Respiratory proteins (e.g. hemoglobin) are present in only a few species. Much less is known about the proteins involved in transport and ion regulation. While serum albumen is absent, it is expected that some protein(s) would serve an analogous function. Several plasma proteins from marine bivalves exhibit non-specific, weak binding to metals such as Cd. High affinity, vertebrate transport/ion regulatory proteins are typically absent, although a histidine-rich glycoprotein (HRG) has been recently isolated from Mytilus edulis and characterized. Mussel HRG is a glycoprotein with a molecular weight of 63 kDa and a PI of 4.8. It is apparently composed of 2 subunits, and is best modelled with 6 high affinity (log K = 7.65) and 10 low affinity (log K = 5.41) Cd-binding sites per molecule. Under environmental conditions, HRG is not saturated with Cd. Further studies are expected to identify additional plasma proteins that are involved in the internal transport of contaminant metals (e.g. Cd) and of physiologically-important elements (e.g. Ca) in bivalve plasma.
Morphodynamics of Bryopa and the Evolution of the Clavagellids

Enrico Savazzi

Department of Earth Sciences, Villav. 16, 75236 Uppsala, Sweden.
E-mail: Enri@pal.uu.se

Facultative semi-endolithic habits are documented in several clavagellids, but Bryopa is the only clavagellid to be fully and obligatorily endolithic. It actively bores in dead calcareous substrates, and the outer surface of its left valve is permanently attached to the wall of the borehole. In spite of this, the bivalve moves forward within the substrate throughout growth. Bryopa achieves these seemingly incompatible feats by sliding forward the soft parts, hinge and right valve within the continuously elongating left valve. The resulting strongly inequivalve condition is unique among clavagellids, as well as endolithic bivalves. Morphodynamics is successful in explaining the morphology of Bryopa as the result of conservative functional, evolutionary and constructional factors coupled with a sudden change in effective environment. In the lack of direct evidence, the evolution of clavagellids from less specialised stocks remains open to alternative explanations. Evolution of tube dwelling clavagellids from burrowing ancestors is as likely as their evolution from a hypothetical, endolithic archaic ancestor. In the latter case, however, Bryopa is probably too specialised to reflect the adaptations of such an ancestor.
Phylogenetic Relationships Of Brackish- and Freshwater Cockles (Cardiidae: Lynmocardiinae)

Jay A. Schneider (1) and Imre Magyar (2)

(1) Department of Geology and Geophysics, University of Wisconsin, 1215 W.Dayton St., Madison, WI 53706 U.S.A. E-mail: jasc@geology.wisc.edu
(2) MOL, Budapest, Hungary

During the Cenozoic, the Tethys seaway became increasingly narrowed due to the breakup of Gondwanaland, and finally resulted in the separation of the Mediterranean, Black, Caspian and Aral seas from the rest of the world ocean. Because of this tectonic activity, various brackish- and freshwater basins existed at the margins of the narrowing Tethys sea (known as the Paratethys) in southeastern Europe and southwestern Asia, primarily from the late Middle Miocene Sarmatian stage through the Late Pliocene Akchagylian stage. Several lineages of molluscs of marine origin, including the cardiid bivalves, underwent one or more diversifications of endemic forms in these restricted basins. A large restricted brackish-water basin developed in the early Sarmatian; amongst this basin’s diverse endemic fauna were cardiids clearly derived from the marginal marine taxon Cerastoderma. This fauna disappeared at the end of the Sarmatian. Freshwater basins developed at the beginning of the subsequent Pannonian stage, resulting in a tremendous diversification of freshwater cardiids throughout the several Paratethyan basins from Austria to Turkmenistan. A phylogenetic link between members of the Sarmatian basin fauna and the Pannonian basin fauna cannot be demonstrated; the Pannonian fauna may have been derived independently from marine Cerastoderma. These freshwater basins and their endemic faunas disappeared in the early Akchagylian (Late Pliocene). The present-day lymnocard fauna lives in marginal marine settings of the Black, Caspian and Aral seas; an origin from a remnant of the Pannonian fauna presently seems more likely than an additional derivation from Cerastoderma.
The Evolution, Adaptation and Ecological Significance of Marine Mytilid Mussels

Raymond Seed and Christopher Richardson

School of Ocean Sciences, University of Wales-Bangor, Menai Bridge, Anglesey, LL58 5EY, U.K. E-mail: r.s@bangor.ac.uk

Mytilid mussels are widely distributed throughout the coastal and estuarine waters of both the northern and southern hemispheres. However, they are especially successful colonisers of flat or gently shelving wave-exposed rocky shores where they often form dense assemblages which can rival tropical rainforests and kelp beds in terms of their productivity. In addition to their potential to become the spatially dominant members within many intertidal and shallow subtidal communities, and their ability, as highly efficient filter-feeding organisms, to act as effective processors of coastal water, mussels form complex three-dimensional matrices which serve as favourable habitat for extremely diverse assemblages of associated organisms containing representatives from virtually all the major invertebrate phyla. Mussels are important as food, not only to humans, but to a wide variety of natural predators. In addition they are highly successful invading species, often of man-made structures, with consequent economic implications, whilst the shells of long-lived individuals can provide valuable historical records of environmental change. This paper will examine the evolution of the mytilid form and consider some of the adaptations exhibited by this extremely successful group of organisms. The ecological significance of mussels, the patterns of biodiversity found within mussel communities from the northern and southern hemisphere, together with the potential value of such communities as environmental biomonitors will also be briefly discussed.
Inoceramids: Last Blooming of an Ancient Stock

A. Seilacher(1), P. Johnston(2) and J.D. Stewart(3)

(1) Department of Geology, Yale University, New Haven, CT 06520, U.S.A.
(2) Royal Tyrrell Museum, Drumheller, Alberta, Canada TOJ OYO
(3) Natural History Museum of Los Angeles County, Los Angeles, CA 90007, U.S.A.

Two discoveries throw new light on the diversification and dominance of Cretaceous inoceramids. (1) A multivincular break ligament, attached to an area formed by the outer shell layer with only tensile components being functional, identifies them as Cryptodonta. An internal fulcrum compensated for the shortcomings of cryptodont hinge construction. (2) A unique baleen-like gill skeleton freed them from the necessity of hanging the gills like curtains. Such key innovations allowed these late cryptodonts to leave the marginal status of small-sized opportunists and to successfully radiate into various soft-bottom lifestyles. Yet, like in rudists, raised levels of ecological specialization drove them to extinction in the face of global changes during the K/T transition.
Cladistic Analysis of Rudist Bivalves

Peter W. Skelton

Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, U.K.
E-mail: P.W.@open.ac.uk

The ‘rudists’ are an extinct group of sessile epifaunal bivalves that flourished in low latitude shelf seas in late Jurassic to Cretaceous times. Their diverse and often bizarre morphologies present a good array of characters for cladistic analysis, though frequent homoplasy has caused some systematic confusion. Informative characters include: shell structures and relative thicknesses of the outer (calcitic), and inner (aragonitic) shell layers; valve asymmetry, and attachment to the substrate; form of the ligament; dentition; and arrangement of the internal shelly supports (myophores) for the adductor muscles, with associated accessory cavities. The last character is especially important for discriminating a number of clades previously lumped into paraphyletic or even polyphyletic taxa in earlier schemes of classification. Suitable outgroups for the analysis are the extinct megalodonts (which share the thick shells and massive dentition of the rudists) and, at a further remove, some living heterodonts. The diagnostic synapomorphy for the clade of all rudists is possession of an outer shell layer of fibrillar prismatic calcite. Within the group, two clades are distinguished according to the attachment of the shell – either by the left valve (including the paraphyletic ‘diceratids’, except for Diceras and Valletia, together with the monophyletic requieniids), or by the right valve (Diceras, Valletia and all other rudists). The monophyletic status of some long-established families is confirmed (e.g. radiolitids and hippuritids), while others are resolved into a number of distinct clades. An important ‘Cinderella’-taxon to emerge from the analysis is that of the polyconitids.
Molecular Phylogeny of Pteriomorph Bivalvia Inferred from 18s rDNA Sequences

Gerhard Steiner

Institute of Zoology, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria.
E-mail: gerh@univie.ac.at

Morphology based phylogenetic studies on higher bivalve taxa are often hampered by multiple cases of parallel evolution in several organ systems (e.g. hinge-ligament system, shell microstructure, gill- and stomach differentiation). The use of the 18S rDNA gene for phylogenetic inference, therefore, seems promising, because it is unlikely to show convergencies due to adaptation to similar ecological niches. 18S rDNA sequence data of 26 pteriomorph and six other bivalve species are presented to assess phylogenetic relationships both among Pteriomorphia and their relationships to other Bivalvia. Trees constructed by Parsimony and Maximum-Likelihood analyses are almost identical. Both Pteriomorphia and Heteroconchia are monophyletic although monophyly of the Autobranchia is not supported. This is probably due to the relatively high overall substitution rate in the Heteroconchia. Monophyletic Protobranchia are the sister group of Pteriomorphia. Low support of the basal pteriomorph branches points to a rapid radiation of five major linages: mytilids, arcids, pinnids, ostreids + pteriids, and a clade containing Plicatula plicata, anomiids, limids and pectinids. Plicatula plicata clusters with anomiids, and limids form the sister-group of pectinids. The position of limids, P. plicata, and the diphyly of Pterioidea suggest a re-elvaluation of homology decisions in several morphological characters.

Chemosymbiosis, Functional Anatomy and Evolution of the Lucinidae

John Taylor and Emily Glover

Department of Zoology, The Natural History Museum, London SW7 5BD, U.K. E-mail: j.ta@nhm.ac.uk

All Lucinidae studied so far possess sulphide-oxidising, chemosymbiotic bacteria contained in modified gill filaments. The ecology, functional anatomy and evolution of the Lucinidae must be considered in relation to this symbiosis. The ctenidia and chemistry of the symbiosis have been extensively studied but other features peculiar to lucinids have received much less attention. We will review the morphological diversity and distribution of living lucinids highlighting features of their functional anatomy including shell and periostracal structures, foot, mantle structures, pallial apertures, palps, ctenidia and gut. Some newly discovered features such as periostracal pipes in Rastafaria will be reviewed. Attention will also focus on the so-called “mantle gills”, plicated structures located near the anterior adductor muscle (Codakia, Phacoides, Lucina) and the probably homologous septum of Anodontia. These are interpreted as secondary respiratory surfaces, their location enabling the separation of incoming oxygenated water from sulphide-rich water. The latter is released from the sediment by the probing activities of the highly elongate foot and is pumped over the gill through the pedal gape and maybe the exhalant tube. The morphology of the Silurian Iliona suggests that the lucinid chemosymbiois is an ancient association.
Growth Patterns of Noetiid Ligaments: Implications of Developmental Models for the Origin of an Evolutionary Novelty among Arcoid Bivalves

Roger D.K. Thomas

Department of Geosciences, Franklin & Marshall College, Lancaster, Pennsylvania 17604-3003, U.S.A. E-mail: r_th@acad.fandm.edu

The dorsal ligaments of arcoid bivalves typically consist of oblique, lamellar and fibrous sheets, alternating along the hinge so their attachments form characteristic chevron patterns. New elements are added at or near the middle of the growth zone as the ligament expands ventrally. Most Palaeozoic arcoids exhibit this growth pattern, which still predominates among their living descendants. In the Early Cretaceous, a novel pattern emerged, with vertical strips of lamellar ligament embedded in grooves in the sheet of fibrous ligament that is attached to each valve. In contrast with the chevron, duplivincular ligament, new elements are added to each end of the noetiid ligament, anteriorly and posteriorly. This distinctive growth pattern is the defining character of the family Noetiidae. Remarkable variation among individuals within populations of a living limopsid arcoid includes forms with vertical strips of lamellar ligament. These variants suggest how the noetiid growth pattern could have been derived from the duplivincular pattern. Computer simulations show that such patterns can be generated by a reaction-diffusion mechanism of the sort first conceived by Turing. Moreover, the noetiid growth pattern can simply be derived from the duplivincular pattern by a developmental switch or change in boundary conditions. These results indicate that striking differences in form may arise from modest changes in developmental process. The evolution of the Noetiidae, members of which are quite disparate in overall shell form, should be reassessed. The derived character on which this family is based may not be uniquely shared, so the group could well be paraphyletic.
Marine Bivalve Ecology: A Key Indicator of Regional Ecological Change in the Tropical American Neogene

Jonathan A. Todd(1) and Jeremy B.C. Jackson (2)

(1) Department of Paleontology, The Natural History Museum, London SW7 5BD, U.K.
E-mail: jon@nhm.ac.uk
(2) Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California, 93027, U.S.A. and Center for Tropical Paleoecology and Archeology, Smithsonian Tropical Research Institute, Panama City, Republic of Panama

The closure of the isthmus of Panama caused large scale ecological changes with evolutionary ramifications across taxa that are just beginning to be understood. Elucidation of the causes and consequences of oceanographic and biotic change through time is the aim of the PPP (Panama Paleontology Project), a multi-taxonomic, international collaborative project. We are sampling complete fossil assemblages from the late Miocene to the Recent in the Caribbean (C) and Eastern Pacific (EP) to track changes and test hypotheses relating to regional faunal change. Here, we interpret habitat change by tracking changes in bivalve ecology, as bivalves are abundant, have a reliable correlation of life habit with shell morphology, and most Neogene genera are still extant. We have bulk-sampled and hand-picked mollusc specimens from 400 sites in four depositional basins, identifying over 200,000 specimens in c. 1000 genera/subgenera (270 bivalves). To minimize sampling artifacts of differential facies occurence through time, we have sampled a wide range of lithologies and water depths within 3 broad time intervals. For comparison with the Recent, we have dredged 60 C and EP sites, using comparable specimen selection techniques. We assess taxon abundances based on collections rather than simple taxon richness extracted from monographs (with the ultimate aim of making these data web-accessible for future research). Our analysis is multivariate, using DCA (Detrended Correspondence Analysis) using ranked and absolute abundance data of the 25 most abundant taxa within the time intervals because the majority of taxa are very rare. We pooled fossil samples within each of three time blocks to control for age-dependent environmental bias (1) Miocene (2) Pliocene (3) Plio-Pleistocene (around final closure), and independently treated the Recent C and EP as ‘time-zero’. Our analyses provided a strong and coherent signal of greater similarity among Recent faunas within an ocean than between oceans. Specifically, the Caribbean is highly divergent from both the Eastern Pacific and their mutual predecessor, pre-closure fauna. This is likely the result of increased regional habitat heterogeneity and changed physical regime. For example, shallow seagrass and well-developed reefal environments simply do not occur in the southern Caribbean until the Plio-Pleistocene – Recent in our Panama and Costa Rican sampling series. Their appearance likely resulted from the decrease in planktonic productivity that followed loss of upwelling in the newly isolated region. Generic /subgeneric diversity has climbed steadily through time, based on cumulative frequency curves, despite the decrease in overall productivity associated with isthmus closure. We attribute this to the increase in habitat heterogeneity and our data challenges assumptions that regional diversity is positively correlated with planktonic productivity.
Early Growth Stages of Carboniferous Pteriomorph Bivalves of the Buckthorn Asphalt (Oklahoma, U.S.A.)

Thomas E. Yancey and Michael J. Heaney

Department of Geology, Texas A & M University, College Station, Texas TX 77843-3115, U.S.A. E-mail: tyan@tamu.edu

Pennsylvanian pteriomorph bivalves recovered from asphalt-impregnated sediments of the Boggy Formation of south-central Oklahoma include individuals with character states rarely seen on Palaeozoic bivalves: prodissoconchs showing PI and PII growth stages, provincular dentition, primary ligament pit, fine shell ornamentation, original shell microstructure, and retention of organic matrix within the shell. Sealing within asphalt retarded diagenesis and prevented shell recrystallization. The PI larval stage is suborbicular for most pteriomorphs of this assemblage, either smooth or with fine concentric ribs. For myalinids, it forms most of the prodissoconch, suggesting lecithitrophy, in contrast to probable planktotrophy for other Buckhorn pteriomorphs. Myalinds as well as an undescribed taxon pass through major metamorphosis and change in shell form upon settlement to a fixed benthic life position, producing an adult shell very different from the larval shell. Preservation of prodissoconch and early juvenile growth stages provides a means of interpreting larval ecology and developmental patterns for myalinids, pterineids, pectinoids (including Chaenocardia), and an unusual undescribed genus. Documentation of the full ontogenic development sequence for Palaeozoic pteriomorphs is limited, but will help to elucidate phylogenetic relationships for ancient lineages within the subclass.
Habitat Requirements of the Anodonta cygnea L. (Bivalvia: Unionidae) in the Nida River Valley

Katarzyna Zajac

Institute of Nature Conservation, Polish Academy of Sciences, Lubicz 46, 31-512 Kraków, Poland. E-mail: noza@cyf-kr.edu.pl

The aim of the study is to determine habitat requirements of Anodonta cygnea in order to save the species and its habitat. The study area was located in the middle Nida river valley (South Poland), which is rich both in natural and the degraded habitat of the species. Main factor responsible for reduction of potential habitats for the species was river drainage. Comparison the water bodies, occupied and unoccupied by Anodonta cygnea, shows that the species prefers larger oxbows or old river channels with slow current. Physique-chemical analyses of water indicate preference for higher oxygen concentration, lower content of NH4, lower conductivity (low content of CaSO4) and lower concentration of Cd in the mussel sites. The number of Anodonta cygnea individuals decreases whereas their body size increases with depth within given water body. There is a significant correlation between number of Anodonta cygnea and depth of silk layer. The current patterns guarantee the highest rate of suspended particles deposition in these places. Water bodies inhabited by Anodonta cygnea arise due to river geological activity. Thus, conservation measures cannot be restricted to small water bodies but must be focused on the protection of the natural character of whole Nida valley.
Molecular Zoogeography of a Deep-Sea Protobranch Bivalve, Deminucula atacellana

John D. Zardus, Michael R. Chase, Michael A. Rex and Ron J. Etter

Department of Biology, University of Massachusetts, Boston, Boston, MA 02125,
U.S.A. E-mail: john@umb.edu

Protobranchs are among the most ancient of bivalves and have radiated extensively in the deep sea, where they dominate the bivalve component of soft-sediment assemblages. Despite their great abundance, molecular investigations of deep-sea protobranchs are lacking because fresh material is difficult to obtain and the DNA of preserved specimens is degraded. To survey genetic variation in several deep-sea protobranch taxa, we developed techniques to extract and amplify mitochondrial DNA (mtDNA) through the Polymerase Chain Reaction (PCR) from museum specimens collected and fixed in formalin nearly 30 years ago. Here we report preliminary data on Deminucula atacellana, a species which ranges on each side of the mid-Atlantic ridge in both the North and South Atlantic Ocean between 1100 to 3900 meters in depth. Haplotypic distributions appear to vary by basin, possibly a consequence of the particular history and physiography of each basin. Within the North American basin, haplotypes segregate along bathymetric rather than geographic gradients. Haplotypes identical to those above 2500m in the North American basin occur at 2900 m in the West European basin. The Argentine basin contains a lineage that is distinct but closely related to those of the North American basin. Collectively, these data suggest that factors in addition to depth influence genetic variation in D. atacellana. Our findings pose intriguing questions about the historical legacy of species and the maintenance of genetic diversity in the deep sea.
POSTERS

Granular Concretions in the Extracellular Tissues of the Freshwater Mussel Hyridella depressa (Hyriidae)

Maria Byrne

Department of Anatomy and Histology F13, University of Sydney, Sydney NSW
2006, Australia. E-mail: mby@anatomy.usyd.edu.au

The Australian freshwater mussel Hyridella depressa forms extensive aggregations of CaP granules in its extracellular tissues. The structure, distribution and elemental profile of these granules was documented by light and electron microscopy. For the elemental study granules were analysed in an X-ray microanalytical study of cryoprepared tissues. The granules are round, electron-opaque and were particularly abundant in the visceral mass and mantle. On surface view, their distribution is readily discerned due to their distinctive orange colour. Iron was a particularly important component of the granules of H. depressa and appears to account for their colour. The granules also contained a number of other elements, with Mg and Mn being common. Trace elements were also present and included
Al, Cu, Zn and Pb. In the mantle and visceral mass the granules form extensive aggregations in the connective tissue and occasionally dominate the tissue space. By comparison, granules were not common in the gills and foot. Considering the pivotal, potentially basal position of the Hyriidae in understanding the evolution and phylogeny of the Unionacea, emphasis was placed on comparison of the CaP granules of H. depressa to those in margaritiferid and unionid mussels. The pattern of granule accumulation in H. depressa was most similar to that described for margaritiferids and contrasted with that described for unionids. The impressive capacity to accumulate and store extensive calcium deposits in their tissues is a unique feature of the Unionacea, but the rationale underlying production of these excess calcium stores is not understood. It is suggested that they may be a by-product of biomineralisation processes in these bivalves in association with their highly efficient Ca- uptake system evolved in conjunction with colonisation of freshwater environments.

Herring Gulls Feeding on Ensis directus, a Bivalve that Recently Invaded the North Sea Area

Gerhard C. Cadée

Netherlands Institute for Sea Research, POBox 59, 1790 AB den Burg, Texel, Netherlands.
E-mail: cad@nioz.nl

Ensis directus, recently succesfully invaded the North Sea. First reported from the German Bight (1979), its spreading was followed regularly. It is now well established on the lower Wadden Sea tidal flats. Soon after its arrival Oystercatchers discovered this new food source. Herring gulls were observed to feed on Ensis mainly during its irregular mass mortalities (winter 1994/95, March 1999). Moribund Ensis then protrude partly from the sediment, unable to reburrow, forming easy prey for Herring gulls. These swim above the deeper part of the tidal flats during low tide, looking sharply around and diving for the protruding Ensis. With the Ensis collected in their beak, they fly to the nearest dry place where they start shaking the shell, still in their beak, vigorously. They drop the shell regularly, trying to sever the adductor muscles and picking at the flesh protruding. Handling time is only 1 – 2 minutes. Sometimes they succeed in consuming the flesh without fracturing the shells. However, some 75% of the shells showed characteristic fractures. In 25% only small pieces were broken from the shell margins near the centre, in another 25% one of the valves was broken near the middle, and in the last 25% both valves were broken near the middle, the valves still adhering by the ligament. The location of the fractures is related to damage by the beak during shaking of the Ensis, not to hammering. Herring gull’s pellets and faeces indicated part of the shell was ingested. Shell dropping from the air was rarely observed.
Cladistic Perspectives on Early Bivalve Evolution

Joseph G. Carter (1), David C. Campbell (1) and Matthew Campbell (2)

(1) Department of Geological Sciences, CB 3315 Mitchell Hall, UNC-Chapel Hill, Chapel Hill, NC 27599-3315, U.S.A . E-mail: cla@email.unc.edu
(2) Department of Geological Sciences, Indiana University, 1005 East Tenth Street, Bloomington, IN 47401, U.S.A.

Phylogenetic analyses of over 300 species of Cambrian – Triassic bivalves, utilizing all available features of shell morphology, hinge dentition, ornament, muscle scars, ligament structure, shell mineralogy, and shell microstructure, give mixed results with regard to replicating commonly accepted suprageneric taxonomic associations. Problems are especially apparent among Ordovician bivalves characterized by transitional dentitions and incomplete data of muscle scars, ligament, and shell microstructure. Silurian and later bivalves, for which data are much more complete, are commonly well resolved into generally accepted clades. A more complete understanding of Early Palaeozoic bivalves and reweighting of individual characters or character suites, especially hinge dentition and shell musculature, will be required to produce a workable, comprehensive phylogenetic classification of the Bivalvia. The next phase of this research will concentrate on refining the character set and testing the effect of character weighting.
On the Model of Periostracum and Shell Formation in Unionidae

Antonio G. Checa(1) and Juan de Dios Bueno-Pérez(2)

(1) Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain. E-mail: ach@goliat.ugr.es
(2) Centro de Instrumentación Científica, Universidad de Granada, 18071 Granada, Spain

The development of the periostracum, from its origin in the periostracal groove until beginning of mineralization at the shell edge, has been studied in three species of unionids. The periostracum consists of a thin outer layer and a thick inner layer, without traces of a third periostracal layer. The outer periostracal layer is the only one formed within the periostracal groove. Growth lines are formed when the outer periostracal layer forms localised folds at the exit of the periostracal groove. In some cases, both flanks of the fold stick together at their inner surface, forming loops. This occurred when growth stopped at the margin while the outer periostracum secretion continued. The excess of this layer contracted and folded at the exit of the periostracal groove (where the periostracum is thinner and weaker). Folds are later sealed at their base by the inner periostracum. The latter layer was secreted outside the periostracal groove, presumably by the internal surface of the outer mantle fold when this extended to the shell tip during mineralization episodes. Its obliquely banded nature and progressive thickening towards the shell edge confirm this. Distally, the periostracum curves back and aragonitic prisms initiate (as spheruliths) within the jelly inner periostracum. In transversal sections, prism growth lines plunge dorsally uninterruptedly across adjacent crystals and continue later into the boundaries between layers of nacreous tablets of the inner shell. This strongly suggests that the mantle causes mineralization when it adheres periodically to the inner surface of the shell growth margin.
Crystallographic Constraints on the Shell Microstructure in Unionidae

Antonio G. Checa(1) and Alejandro Rodríguez-Navarro(2)

(1) Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain. E-mail: ach@goliat.ugr.es
(2) Instituto Andaluz de Ciencias de la Tierra, CSIC-Univ.Granada, 18071 Granada, Spain; Present address: Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, U.S.A.

Unionid shells consist of a thick periostracum, an outer aragonitic prismatic layer and an inner, thicker nacreous layer. Prisms begin to grow within the internal periostracum, and each prism is an aggregate of fibrous crystals, which initiate near the prism centre in parallel to its long axis to later radiate progressively outwards. When fibres of adjacent crystals meet, those running faster laterally (i.e., oriented more transversely) compete successfully for space and progressively displace their neighbours. During growth, small prisms are more prone to disappear and only a few, evenly-sized prisms survive. To explain this process, one has to consider that in bivalves (and molluscs in general) the mantle limits the growing surface of the shell and that prisms always grow perpendicular to the mantle surface (from which essential constituents are provided). Prism-forming fibres expand transversely and become wedge-shaped in cross section with growth, so that stacking of these units along the prism causes fibres to become progressively more parallel to the long axis of the prism. The transition to the nacreous layer occurs when only a few, big-sized and slightly diverging fibres remain. We suggest that nacreous tablets represent a more stable growth for a common orientation of the long axes of the fibres. Nacreous tablets are uniformly oriented with their fastest growth direction (‘b’ axis) pointing perpendicular to the margin (the growth front). This preferential orientation allows crystals to advance more rapidly perpendicular to the growth front, therefore outcompeting neighbours with other orientations.

A New Book on the Marine Bivalvia of the Northeastern Pacific Ocean

Eugene V. Coan and Paul Valentich Scott

Department of Invertebrate Zoology, Santa Barbara Museum of Natural History,
2559 Puesta del Sol Road, Santa Barbara, California 93105, U.S.A. E-mail:
gene@sierraclub.org; pvsc@sbnature2.org

Features of our recently completed manual on the marine bivalves of the northeastern Pacific Ocean are reviewed. The book covers the region from northern Baja California to the Alaskan Arctic, and includes descriptions and illustrations of bivalves from the intertidal zone to abyssal depths. Development of the final manuscript took almost ten years after it was received from the late Frank R. Bernard. A particular effort has been made to ensure the book’s utility to those with an interest in the Bivalvia outside its ostensible geographic area. A conservative taxonomic approach was adopted, with minimal use of subgenera. Without substantial evidence to document their distinctness, many taxa are regarded as synonyms. Important problems remain for workers to resolve with modern methodologies.

Bivalve Palaeoecology in an Early Cretaceous Carbonate Ramp, Central Argentine Andes
Susana E. Damborenea, Miguel O. Manceñido and Alberto C. Riccardi

Departamento Cientìfico Paleontología Invertebrados, Museo de Ciencias Naturales La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina.
E-mail: susa@mmance.cyt.edu.ar

On the eastern slope of the central Argentine Andes crop out extensive Early Cretaceous deposits accumulated within the Neuquèn basin. This study is focused on the benthonic faunas from the Berriasian-Hauterivian interval that occur in mostly carbonate units of the Mendoza Group. Eighteen localities were sampled over a N-S strip, 230 km long, between Diamante and Grande rivers in southern Mendoza Province, western Argentina, and the qualitative faunal composition along the stratigraphic sections surveyed was recorded. Although the identified fauna also includes cephalopods, brachiopods, gastropods, corals, echinoderms, serpulids and crustaceans, bivalves are by far the most abundant and diverse invertebrate group, thus allowing the characterisation of various assemblages of palaeoecological significance. The biostratigraphic control was provided by co-occurring ammonites. On this basis, the distribution in time and space of about fifty bivalve species was subjected to multivariate analysis and sets of recurrent groups of taxa were recognized. Interpretation of such fossil associations was based on the analysis of biofacies, trophic groups, spatial distribution of guilds, as well as relationships to lithofacies and inferred oxygen levels. One of the main fossil associations showing a localized occurrence is related to coral buildups, whereas several oyster-dominated associations are widespread in most other carbonate lithofacies. On the other hand, mud grade lithofacies bear distinctive, thin-shelled bivalve associations, which developed basinward. A palaeoenvironmental model for this part of the basin during Berriasian-Hauterivian times involves a carbonate ramp with occasional development of organic banks.
Jurassic Bivalves of the Iberian Range (Spain)

Graciela Delvene

Paleontologia, Dpto. Ciencias de la Tierra, Universidad de Zaragoza, 50009, Zaragoza, Spain. E-mail: gdel@posta.unizar.es

The aim of this paper is to illustrate the poorly known Middle and Upper Jurassic Bivalves of the Iberian Range, their distribution and their relative abundance. Study area is the northeastern Iberian Range, provinces of Teruel and Zaragoza. The dominantly carbonate sediments and were deposited in a shallow to temporarily emerged palaeogeographic high on the outer Aragonese Platform. The sediments are Callovian-Oxfordian in age and belong to the Chelva and Yatova formations. 15 species of the genera Modiolus, Cingentolium, Camptonectes, Chlamys, Atreta, Ctenostreon, Plagiostoma, Pseudolimea, Myoconcha, Unicardium, Anisocardia, Pleuromya, Pholadomya and Actinostreon have been identified.
In the most fossiliferous section the following species are most abundant: Ctenostreon proboscideum (J. Sowerby), Plagisotoma aff. calvata Zakharov, Myoconcha (Myoconcha) cf. ratheriana d´Orbigny and Pholadomya (Bucardiomya) protei (Brongniart). Infaunal bivalves are always preserved as articulated internal moulds, many of them in life position (Pholadomya, Pleuromya). Semi-infaunal bivalves are articulated, some of them in shell, others in steinkern preservation. Among epifaunal bivalves, the majority of the limids (Ctenostreon, Plagiostoma) are articulated. The reminder is preserved as disarticulated shells. Approximately, half the specimens lived epifaunally, predominantly byssally attached. The other half were infaunal and semi-infaunal (endobyssate), with deep burrowing bivalves (Pholadomya) dominanting. All bivalves were suspension-feeders. Infaunal, semi-infaunal and some epibyssate bivalves are autochthonous. The bivalve association represents the relict of a community that lived in a shallow marine low energy environment, possibly subject to occasional disturbance by high energy events. Sedimentation took place by suspension. The substrate was enough soft for infaunal bivalves. Byssally attached bivalves could fix themselves to the very abundant ammonite shells.

This work is a contribution to the project P35/97 (Government of Aragón, Spain).
Australobuchia in the New Zealand Late Jurassic

Dan Hikuroa

Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: d.hi@auckland.cic.nz

Ferdinand von Hochstetter reported Buchia plicata (Zittel) in 1864 and subsequently additional fossil buchiid species have been described from New Zealand ranging in age from Middle Heterian to late Puaroan (Late Oxfordian to Late Tithonian). Fleming recorded the Oxfordian-Kimmeridgian Buchia malayomaorica (Krumbeck) from Kawhia and noted a form of Puaroan age (mid to Late Tithonian) as being perhaps closer to the Indonesian B. misolica (Krumbeck). Jeletzky erected Malayomaorica for B. malayomaorica and tentatively included in it B. misolica and Fleming’s B. aff. misolica. Zakharov proposed Australobuchia for the southern Buchia, because they lacked both a true Ogelenkgrube, and an alivincular ligament. Three buchiids, B. aff. misolica, B. hochstetteri Fleming and B. plicata, are known from Puaroan rocks at Port Waikato, south Auckland, New Zealand, where they form three contiguous biozones, B. aff. misolica, the oldest and B. plicata youngest. The Puaroan has been divided into substages, the Mangaoran and the younger Waikatoan, based on belemnites. B. aff misolica occurs across their mutual boundary in strata from Port Waikato to Kawhia, a distance of c.100 kilometres. This study has determined that the specific features of B. aff. misolica and the New Zealand Tithonian buchiids confirm Zakharov’s separation of Australobuchia. This raises the issue of bipolarity and the question whether the ancestry of Australobuchia lies in Malayomaorica, Praebuchia or elsewhere.
The Basket Shell Corbula gibba (Olivi, 1792) (Corbulidae, Bivalvia)

Mirjana Hrs-Brenko, Medacovíc Davor, Labura Zeljka and Pisarovíc Anamarija

Rudjer Boskovíc Institute, Center for Marine Research, Paliaga 5, HR-52210 Rovinj, Croatia. E-mail: bre@cim.irb.hr

Samples of the basket-shell, Corbula gibba (Olivi, 1792), were taken from biocoenological surveys carried out in the northern Adriatic Sea from 1982-1992. A total of 23,975 Corbula individuals were examined during the study period. Distribution, population density, size frequency distribution, recruitment, growth and mortality rates were investigated. Data show a wide distribution and abundance of Corbula with stable population structure in the communities of silty sand and muddy gravel bottoms under environmental stresses. Successful survival rates during bottom oxygen crisis, followed later by an abundance of new recruits into destroyed bottom communities, point out on a high Corbula reproduction potential that is feasible in the absence of bivalve food and space competitors and predators. Consequently a dominance of many basket shell juveniles in an investigated sample could be a valuable sign of the occurrence of a very recent bottom disaster.

Ontogenetic Changes of Boring Behaviour in Barnea manilensis (Pholadidae)

Yasuhiro Ito

University Museum, University of Tokyo, Tokyo 113-0033, Japan. E-mail: ito@um.u-tokyo.ac.jp

Barnea manilensis (Philippi, 1847) is a common bivalve of the superfamily Pholadoidea characterized by ability to bore into a variety of substrata. It bores into soft rock (e.g., mudstone and shale) of the intertidal zone and in Japan, occurs from Hokkaido to Okinawa. In the present study, ontogenetic changes in morphology related to boring behaviour by B. manilensis were observed. The boring is initiated by metamorphosis. The pediveliger does not bore but crawls with a simple set of movements. The boring ability is acquired by adding step, boring movement, to the crawling sequence. The boring style exhibited by the movement changes with growth. During the transition from pediveliger to juvenile stages, the shell outline changes from round to elongate. Along with such a morphological change, the boring style gradually changes from anterior boring in early, round-shelled, juveniles, where the opening of the anterior valve margin, with rotation around a dorso-ventral axis, abrades the burrow wall, to ventral boring in older and larger, long-shelled, individuals, which open the ventral margin, with rotation around a longitudinal axis (hinge line) for abrasion. This study, with an examination of the literature, leads to the suggestion that early juveniles of all pholads employ anterior boring. Later, many pholads continue anterior boring throughout life, whereas others gradually shift towards ventral boring. In addition, anteriorboring is thought to be a primary character of pholads, and ventral boring aspecialized character derived from anterior boring.
Aggregations of Gastrochaena (Bivalvia) in Dead Parts of Live Scleractinians from the Red Sea

Karl Kleemann

Department of Palaeontology, University of Vienna, Althanstr. 14, A-1090 Vienna,
Austria. E-mail: Karl@univie.ac.at

Veligers of Gastrochaena species, settling on dead parts of live scleractinians, chemically penetrate the coral skeleton after metamorphosis (Kleemann 1995 and cited references). The bivalves also secrete calcareous tubes around their siphons, thus maintaining contact with the water body. Later, when surrounded by living tissue due to lateral growth of the
corals, the impression may be created that the bivalves also attack live coral (Kleemann 1980). Aggregations of Gastrochaena in dead parts of live scleractinians from the Red Sea are documented by in situ photographs. The infested corals were mainly of the massive growth type, Favia, Favites, Acanthastrea, Leptastrea, Leptoria and Platygyra, but also included a tangle of Acropora branches. The used frame size measured 19 x 13 cm and covered a plane area of 247 cm. Within this, the amount of Gastrochaena-infested dead area is usually much less, amounting to 4 – 180 cm. The number of Gastrochaena siphonal openings ranged from 1 – 26 in the samples. The relative abundance of siphons ranged from 1.12 – 14.82 cm-2. Size classes of siphon-openings ranged from 0.02 – 0.48 cm-2. The presented examples clearly reveal the characteristic figure-of-eight openings of the calcareous siphons of Gastrochaena. This is particularly evident, when the siphonal tissue is not fully expanded and the white rim of the two adjacent dark orifices forms a distinct figure-of-eight. When several such figures are positioned close together, different size classes can often be noted. In such cases, obviously more than a single spat fall had occurred. Were these occurrences, leading to aggregations, merely accidental or were
triggering factors involved? As no similar aggregations were noted in large dead coral areas, the observed distribution in mainly live coral habitats may be a result of restricted substrate for settlement. A disadvantage of aggregation can be expected due to competition for food rather than space, as gastrochaenid borings generally do not cross each other, in contrast to those of lithophagids (Kleemann 1974). On the other hand, the different size classes of Gastrochaena siphons next to each other may be a result of veligers settling in the vicinity of successfully established conspecifics. A likely advantage of such a possible behaviour would be simultaneous spawning and the probability of producing more larvae in the sea, and thus, a higher reproduction potential.
The Immigration of Ensis americanus Gould, 1870 and Petricola pholadiformis (Lamarck, 1822) into the North Sea-Baltic Transition Area (= Danish Waters)

Jørgen Knudsen

Zoological Museum, Universitetsparken 15, 2100 Copenhagen, Denmark

Both immigrants are natives of the east coast of North America. Ensis americanus made its first appearance in western Europe in 1979, when it was found in large numbers on a brach of the German North Sea coast. Presumably the population originated from larvae released from the ballast tank of a ship, and the invasion probably took place 4-5 years before. In 1981 it had spread into the adjacent Danish Wadden Sea, and in 1982 E. americanus was recorded from the coast of Skagerak. In 1984 it was found in the Kattegat and in 1988 in the Belt Sea. In 1994 it was recorded from the western Baltic. E. americanus is now common in many parts of the Transition Area, living mainly at depths of 2-5 meters. On several occasions huge numbers of empty valves, both single and conjoined, have been washed ashore. Veligers and metamorphosed juveniles are common in the Transition Area.
In 1890 Petricolis pholadiformis was found in a locality on the southeast coast of England, where American oysters had been relaid. By 1905 P. pholadiformis had spread to the Netherlands and to the Danish Skagerak coast. The immigration into the Transition Area had the following course: 1931, the northern part of the Transition Area and in 1943, the southern part. Some 30 marine invertebrate immigrants are recorded from the Transition Area. Most of these first appeared in western Aurope in the English Channel and adjacent waters. Their invasion into the Transition Area is facilitated by the north-going current along the Danish North Sea Coast.
Morphological Character Analyses using PAUP in Small Freshwater Clams (Eulamellibranchiata, Sphaeriidae)

Alexei V. Korniushin and Matthias Glaubrecht

Institut fuer Systematische Zoologie, Museum fuer Naturkunde, Invalidenstr. 43, D-10115 Berlin, Germany. E-mail: fran@rz.hu-berlin.de

Sphaeriidae is a freshwater bivalve family with world-wide distribution and wide spectrum of ecological preferences. The group is important both in fundamental and practical aspects, but ignored in many biogeographical and environmental studies because of problems in its systematics, particularly because of the scarcity of available taxonomic and diagnostic characters. The family is traditionally divided in 2 subfamilies: Sphaeriinae (with the
genera Sphaerium, Musculium and Pisidium) and Euperinae (comprising Eupera and Pseudanodonta). However, classification on the lower levels is confusing. Amendments suggested recently by different taxonomic schools are contradictory and none of them is supported by any parsimony analysis. The basis for the present investigation is greatly enlarged by anatomical studies carried out in the last years and covering the whole distribution range of the group. In addition to the traditional shell characters, data on mantle, gills, alimentary canal, nephridia and breeding organs are now available for 8 species of Sphaerium, 10 species of Musculium and 38 species of Pisidium. For our analyses we use also 2 species of the subfamily Euperinae and 1 species of the family Corbiculidae (as outgroup). The arrangement of siphonal retractors and radial mantle muscles, the position of the outer demibranch and the configuration of the dorsal lobe
of the nephridium are utilized in phylogenetic analysis for the first time. We apply two different coding approaches, reductive and composite coding, that result in 2 character lists, of 68 and 43 characters, respectively. The first results of the phylogenetic analyses by PAUP will be presented and their implication for systematics, evolutionary studies and
biogeography will be discussed.

Investigation is supported by the A. von Humboldt Research Fellowship.
Functional Anatomy of the Digestive System of Neoteredo Reynei (Bartsch, 1920) and Psiloteredo Healdi (Bartsch, 1931) (Teredinidae) *

Sônia Godoy Bueno Carvalho Lopes (E-mail: soni@uol.com.br)
Osmar Domaneschi(+) (E-mail: doma@ib.usp.br)
Daniela Toma de Moraes (E-mail: dtmo@ib.usp.br)
Marisa Morita (E-mail: marc@sti.com.br)
Georgeana Lima Curi Meserani (E-mail: mese@ib.usp.br)

Departamento de ????, Universidade de São Paulo, Caixa Postal 11461, CEP 05422-970, São Paulo (SP), Brazil

Studies on the internal anatomy and functioning of the stomach in Teredinidae are still restricted, although useful for a better understanding of the correlation with the ability of these bivalves to feed mainly on wood or suspension. This is the scope of the present work, considering the Teredininae Neoteredo reynei and Psiloteredo healdi, two common species in the Brazilian mangroves. Neoteredo reynei and P. healdi have globular type of stomach, considered less specialised to deal with wood, compared with the elongated type. The internal anatomy and functioning of the stomach are similar in these two species. Both have normal and specialised digestive diverticula, the latter very reduced comparatively to the normal one. Outstanding differences are related to the larger size of the right caecum and semi-spiral conical projection, the well developed appendix and respective typhlosole, and the enormous anal canal, always full of wood in N. reynei. The appendix and respective typhlosole of P. healdi are usually conspicuous in small specimens, but extremely reduced in diameter and lacking typhlosole in large animals. The anal canal is always a short and narrow passage for the faecal pellets. The characteristics of the appendix and anal canal of N. reynei suggest that these structures could be special sites for digestion of wood and that the species depends mainly on this source of food, despite the globular type of stomach and small amount of specialised digestive diverticula. The characteristics of digestive system of P. healdi indicate predominantly suspension feeding habit.

(*) Financial support: “Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
(+) Supported by the CNPq
Conservation of the Depressed River Mussel, Pseudoanodonta complanata

Anna McIvor and David Aldridge

Department of Zoology, Downing Street, Cambridge, U.K. E-mail: alm1@hermes.cam.ac.uk

Pseudanodonta complanata (Rossmässler) is the rarest British unionid. It is on the priority list of the UK Government’s Biodiversity Action Plan, and is considered threatened in Austria, Germany, Poland, Sweden and Switzerland. This study has three main aims: to identify its habitat requirements using within and between catchment distributions, to study the reproductive biology and identify host fish species, and to monitor the effects of waterway management on P. complanata in order to develop viable conservation strategies.
Application of Visual Census for the Study of Bivalve Distribution in Saltwater Lake Malo Jezero (Mljet National Park, South Adriatic Sea)

Melita Peharda (1), Mirjana Hrs-Brenko (2), Danijela Bogner (3), Vladimir Onofri (1),
Davor Lucic (1), Adam Benovic(1)

(1) Institute of Oceanography and Fisheries, Laboratory Dubrovnik, P.P.Box 83, 20000 Dubrovnik, Croatia. E-mail: mel@labdu.izar.hr
(2) Rudjer Boskovic Institute, Center for Marine Research, G. Paliaga 5, 52210 Rovinj, Croatia
(3) Institute of Oceanography and Fisheries, P.O.Box 500, 21000 Split, Croatia

Visual census of easily visible bivalve species and collection of surface sediment was preformed by scuba diving along four transect lines in saltwater lake Malo jezero, Mljet National Park during summer of 1998. Statistically significant difference in distribution of Pinna nobilis (Kruskal-Wallis = 13.363, P = 0.004), Arca noae (Kruskal-Wallis = 12.929, P = 0.005) and Chlamys glabra (Kruskal-Wallis = 16.667, P = 0.001) was found with respect to depth. No Pinna nobilis was found at depths greater than 15 m (maximum depth of a lake is 29 m). For species Chlamys varia, Ostrea edulis, Modiolus barbatus, Chama sp. and Gastrochaena dubia only presence/absence data were collected. For all species observed it was found that as depth increases, the number of bivalves decreases. Sediment analyses showed that at depths between 15 and 20 m percentage of sand in the sediment sharply decreases while the percentage of mud increases. Observed change in sediment composition correlate with changes in bivalve distribution. Survey method used in this study is non-destructive and relatively simple to perform and as such can be used for monitoring long term changes in bivalve distribution.

Revision of the Australian Condylocardiidae

Peter Middelfart and Winston Ponder

Department of Malacology, The Australian Museum, 6-8 College Street, Sydney, NSW 2000, Australia. E-mail: Pet@amsg.austmus.gov.au

Australian condylocardiids are being redescribed and revised. This family of minute carditoideans has so far been poorly described and illustrated, rendering identification very difficult or even impossible. In addition, nothing is known about the biology of these tiny bivalves other than most species appear to be free living in sediments and brood a small number of relatively very large embryos. The current revision employs Scanning Electron Microscopy for the examination of the taxa, an ideal tool for illustrating these minute animals. Basic anatomical studies, as well as meristic and phylogenetic analysis, will be used to provide a robust taxonomy of the group. Eleven genera, in two subfamilies (Condylocariinae and Cuninae) are currently recognised in Australia, viz., Condylocardia, Benthocardiella, Condylocuna, Cuna, Cunanax, Hamacuna, Micromeris, Particondyla, Radiocondyla, Saltocuna, and Volupicuna, comprising forty seven species, of which many are endemic. From our preliminary examination of the material in the Australian Museum collections at least 30% of the species are undescribed, bringing the actual species total for Australia to about 60. This study is part of a larger taxonomic revision of several groups of small Australian bivalves, including, in addition to the Condylocardiidae, the Galeommatoidea (“Leptonidae”, “Erycinidae”, “Kellidae”, etc.), Cyamiidae, Sportellidae, and Neoleptonidae. All the families contain small notoriously taxonomically difficult taxa, of which about 160 species are currently recognised in the Australian fauna.
The Factors Affecting Fertilization Success in the Free-Spawning Antarctic Soft-Shelled Clam, Laternula elliptica

Dawn Powell(1), Paul Tyler(1) and Lloyd Peck(2)

(1) School of Ocean and Earth Science, Southampton Oceanography Centre,
University of Southampton, U.K. E-mail: dkp@soton.ac.uk
(2) British Antarctic Survey, High Cross, Madingley Road, Cambridge, U.K.

Recent research has revealed that many common Antarctic marine invertebrate species reproduce by free-spawning their gametes directly into the sea, with some species spawning in the austral winter when temperatures are as low as -1.8ºC. The infaunal Antarctic clam, Laternula elliptica, is an example of a free-spawner which generally spawns in the austral winter. Laboratory trials were conducted in Antarctica on the factors affecting fertilization success of the gametes of this species. Fertilization success was found to be highly dependent on the sperm density. A distinct peak in fertilization success was consistently replicated at a very high sperm concentration of 107-108 sperm ml-1. The clam exhibited extremely low fertilization rates (<10% fertilization success) when the sperm concentrations fell below 106 sperm ml-1 (similar values were also found in the Antarctic limpet, Nacella concinna). This is in contrast with studies on temperate, tropical and deep-sea free-spawning invertebrates which show a degree of fertilization success at values as low as 102-103 sperm ml-1 with the highest success rates occurring at values of 105-106 sperm ml-1. The results for the Antarctic species could indicate a higher energetic cost to reproduction in the cold Antarctic waters and explain some of their reproductive strategy. An increase in abnormally developing larvae was noted in L. elliptica above 107 sperm ml-1 indicating the occurrence of polyspermy. However, the costs of producing a high quantity of sperm could be balanced by the quality of the spermatozoa. Fertilization of fresh ova was still possible over 85 hours after the initial sperm release. Temperature and salinity were found to affect fertilization success at the 107 sperm ml-1 concentration. Gametes exposed to a temperature range from -2ºC to +5ºC showed the fertilization success of normally cleaving embryos to be >80% between -2ºC to 0ºC, followed by a sharp decline in success at temperatures above 0ºC, with no normal development occurring at +5ºC. However, abnormally fertilized embryos were seen to increase at +3ºC from around 5%, to almost 20% at +5ºC. Over a salinity range of 33 to 25, around 90% fertilization success occurred between 33 and 31, but dropped sharply to 50% at 28, <10% success at 26 with no fertilization occurring at 25. Therefore, even when sperm concentrations are at an optimum level for a high success rate, factors such as increased seawater warming and ice melting could lead to a serious decrease in fertilization success and ultimately, to larval recruitment, as well as acting to delimit the geographical range of this mollusc species. The implications of these results are discussed.
Shell Drilling by the Necklace Shell Euspira catena and Polinices pulchellus (Gastropoda: Naticidae)

Christopher Richardson, Leanne Butcher, Peter Kingsley-Smith and Ray Seed

School of Ocean Sciences, University of Wales – Bangor, Menai Bridge, Anglesey, LL59 5EY, U.K. E-mail: oss@sos.bangor.ac.uk

Naticid gastropods Euspira (=Polinices) catena (max. size 30mm) and Polinices pulchellus (=P. polianus) (max. size 15mm) are voracious predators of bivalves. They are patchily distributed in sand and sand/mud habitats subtidally in the coastal waters of North Wales where they feed mainly on Fabulina fabulina, Angulus tenuis, Abra alba and Nucula nucleus. Other bivalves including Parvicardium scabrum, Donax virgatus, Chamelea gallina, and Venus verrucosa are less frequently attacked. Drill holes in a death assemblage of bivalves from Red Wharf Bay indicated that 25% of the population had been attacked. More than 50% of drill holes occurred in the anterior (umbone) region in A. tenuis, A. alba and N. nucleus whilst in the more elongate shell of the tellin F. fabulina drill holes were distributed across the entire shell surface. When small (<15mm) intertidal cockles Cerastoderma edule, were offered to these naticids in laboratory experiments 75% of drill holes occurred around the anterior rather than the posterior area of the umbo, whereas larger cockles (>15mm) were drilled equally in the anterior and posterior regions. Distances between drill hole and umbo were linearly related in cockle prey <15mm but with increasing prey size the drill hole was positioned closer to the umbo. Acetate peel replicas of shell sections from 5-25mm drilled cockles revealed that shells <10mm were of uniform thickness (0.1-0.2mm) along their length whereas shells >20mm were thin at the umbo (0.1mm) increasing progressively in thickness towards the shell margin (1.1mm). Laboratory video observations of naticids presented with different sized cockle prey demonstrated that prey handling times were extremely variable (18-100min) whilst drilling times (20-24 h) did not differ significantly. There was no relationship between the position of the underlying digestive gland and drill hole in C. edule. It is suggested that when naticids are feeding on different shaped and sized bivalve prey they select the thinnest and hence most energy efficient position for drilling. Results of this study suggest that it should be possible to predict the size range of naticid predator from the position of the drill hole and the size of the prey attacked during drilling and this may have palaeoecological significance.
New Anomalodesmatan Bivalves in Life Position from the Rhenish Devonian (Germany)

Nicole S. Rogalla and Michael R. W. Amler

Institut für Geologie und Paläontologie der Philipps-Universität Marburg Abt. Invertebraten-Paläontologie, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
E-mail: roga@stud-mailer.uni-marburg.de

Bedded carbonaceous siltstones of Middle Devonian (Givetian) age from the Eifel Mountains (Western Germany) have yielded a remarkable sample of extremely elongated, articulated bivalves preserved in life orientation. The specimens are accompanied by a single left valve embedded horizontally in the bedding plane and further isolated by articulated shells. Combination of all the information given by the specimens allowed the reconstruction of the complete morphology and the most likely life orientation. The very distinctive morphological features of the specimen, e.g. the unusual length of the fossils (>15 cm), the increase in height in posterior direction, the posteriorly gaping valves, a very shallow ventral sinus, the minute umbones, an external shell sculpture consisting of comarginal fila and few obscure oblique radiating lines, the shape of the anterior adductor and the weak posterior adductor as well as the edentulous hinge and the elongate opisthodetic parivincular ligament, do not allow an assignment to any genus described up to now. However, this attempt of linking the specimens with any remarkably elongated Palaeozoic bivalve species focussed on a discussion of the evolution of “sword-shaped” bivalves in the Early and Middle Palaeozoic. Posteriorly elongated bivalves of the Palaeozoic have been classified as either being members of the subclass Isofilibranchia or the Anomalodesmata. Since the phylogeny of anomalodesmatans and isofilibranchs is difficult to unravel, the definition and composition of both have been vividly discussed recently by several authors (e.g. Runnegar 1974, Pojeta 1978, Johnston 1993, Cope 1996, 1997). Our Middle Devonian bivalves seem to combine characters of the orthonotids and the modiomorphids. In concurrence with the opinions of Cope and Johnston we suggest their assignment to the family Orthonotidae within the order Pholadomyoida of the Anomalodesmata (Amler 1999). They retained few modiomorphid characters which may have been their early ancestors and preferred an endobenthonic (?endobyssate) life position with an angle of about 60-70° to the substrate surface. As there is no indication of a sinus in the pallial line either a direct contact of the posterior mantle edge with the sea water within the exposed posteriormost part of the shell or non-retractable siphons seem to be the most likely life habits. In evolutionary view, no direct descendents of Late Devonian or Early
Carboniferous age are known.

Temporal Change of Life-History Traits in Fossil Bivalves: An Example of Phacosoma japonicum from the Pleistocene of Japan

Shin’ichi Sato

Department of Geology, National Science Museum; 3-23-1 Hyakunin-cho, Shinjuku-ku, Tokyo 169-0073, Japan. E-mail: kuro@kakaku.go.jp

Shell microgrowth and oxygen isotope patterns were examined in fossil specimens of a venerid bivalve Phacosoma japonicum from the Kami-iwahashi shell bed (c. 2.5 m thickness) in the Middle Pleistocene Shimosa Group (c. 0.2 Ma) in central Japan. Winter and spawning breaks in this species can be distinguished by the shell microgrowth analysis, and oxygen isotope values are high near winter breaks and low around spawning breaks. These breaks, therefore, can be used to estimate age of sexual maturity and shell growth rate in fossil specimens. Shell microgrowth analysis in the three fossil samples from the lower, middle and upper horizons among this shell bed reveals that the maximum shell height and age of sexual maturity decrease gradually toward the top of this shell bed. Also, extant populations around the Japanese coast show a progressive change of life-history traits along a north-south gradient. Life-history traits of the fossil sample from the lower horizon of this shell bed resemble those of the extant population from Ishikari Bay, Hokkaido, northern Japan, and those from the upper horizon of this shell bed are similar to those of the extant population in Tokyo Bay, central Japan. The geographic variation of life-history patterns among the living populations is related to the difference of mean water temperature during the growing season for each population. The temporal change of life-history traits observed in the fossil samples, therefore, reflects the increase of mean annual water temperature during the deposition of this shell bed.
The Upper Jurassic of N-Germany – Taxonomy of Bivalves and Gastropods from the Environs of Hildesheim

Henning Scholz

Institute for Palaeontology of the University of Würzburg, Pleicherwall 1, 97070 Würzburg, Germany. E-mail: henn@mail.uni-wuerzburg.de

The benthic macrofauna of the Upper Jurassic of N-Germany has hardly received any attention in the last few decades. Classic studies about the area reach back to the last century. Thus a revision this fauna was long overdue. The results here presented are part of my diploma thesis. The fossils (about 2000 bivalves and 1100 gastropods) available for study were collected by Prof. Dr. H. Sturm mainly during extension of the motorway A7 Kassel – Hannover near Hildesheim. The city of Hildesheim lies in the Leine- and Weser-Highlands approx. 30 km south of Hannover. In the Upper Jurassic, the area of the Leine- and Weser-Highlands was covered by a shallow epicontinental see. The main fossil-layer at the site of roadworks near Hildesheim, which yielded about 2200 fossils, stratigraphically belongs to the Upper Oxfordian (Humeralis-Beds and Upper Korallenoolith respectively). The thickness of the Upper Korallenoolith in the Hildesheim area is approx. 60-70 m. A taxonomic study of the fossils resulted in identification of 74 bivalve taxa (12 of them in open nomenclature) and 32 taxa of gastropods (seven of them in open nomenclature). Only 38 of the altogether 106 taxa have been described from Northern Germany so far. Many of the other taxa are known up to now only from southern, northern or western Europe. This example illustrates the problem faced by palaeobiogeographers: Even in apparently well-known classical areas the biota are far from being completely known!

A New Commensal Bivalve Mollusc from the Northeast Pacific Ocean

Paul Valentich Scott (1) & Diarmaid Ó Foighil (2)

(1) Department of Invertebrate Zoology, Santa Barbara Museum of Natural History, 2559 Puesta del Sol Road, Santa Barbara, California 93105, U.S.A.
E-mail: pvsc@sbnature2.org
(2) Museum of Zoology, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan 48109-1079, U.S.A. E-mail: diar@umich.edu

A galeommatoidean bivalve mollusc, representing a new genus and species, has been discovered off the coasts of southern California and Vancouver Island, British Columbia. The new bivalve has a commensal relationship with the heart urchin, Briaster latifrons (A. Agassiz, 1898). It has been observed crawling between the ventral spines of this urchin, frequently near the anal fasciole. The bivalve has been recorded from the intertidal zone to 444 meters depth, in muddy sediments. In common with other galeommatoideans, this species broods its young, however it differs from the majority of it commensal confamials in that it appears to lack a planktotrophic larval ontogeny. Several galeommatoidean bivalves have been recorded in association with other echinoids, in particular with the urchins Echinocardium and Spatangus. The new northeastern Pacific bivalve has few morphological similarities to these commensal species described from the Atlantic, northwest Pacific, and Australia. The new species has gross morphological similarities to members of the genus Divariscintilla Powell, 1932, from New Zealand and the south-eastern United States. However, we found differences in the prodissoconch, hinge, shell thickness, foot, mantle tentacles, and the larval development of this species that necessitate placing it in a separate genus.
Cladistic Analysis of Rudist Bivalves

Peter W. Skelton

Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, U.K.
E-mail: P.W.@open.ac.uk
Perumytilus purpuratus and Mytilus edulis, and their Associated Macroinvertebrates

Kate Smith, Ray Seed and Christopher Richardson

School of Ocean Sciences, Menai Bridge, Anglesey, LL59 5EY, U.K. E-mail: osp@bangor.ac.uk

This presentation will consider mussel beds from wave exposed rocky shores in Central Chile (Perumytilus purpuratus) and in North Wales (Mytilus edulis). The growth rates and age structure of several mussel populations from wave exposed shores are described from the seasonal patterns of microgrowth bands present in the outer prismatic layer of the shell. Within these populations the maximum age of Perumytilus purpuratus was nine years and in Mytilus edulis seven years, whilst the maximum size recorded for these species was 37.9 mm and 37.4 mm respectively. In both geographical locations, growth rate was related to tidal elevation and degree of wave exposure. The more wave exposed sites generally contained a wider age range of mussels compared with those from sheltered conditions or at sites impacted by human activities (e.g. mining activities), where mussels were younger and had a restricted size distribution. The macroinvertebrate fauna associated with these mussels were investigated and analysed using the PRIMER package. Populations of both contained approximately 60 taxa with representatives from most of the major phyla. Significant differences were observed between mussel communities from the two geographical regions; thus, whilst several species of gastropods were associated with P. purpuratus, these were absent from the M. edulis community. Faunal diversity in the P. purpuratus community was depressed at sites subjected to human impact. Mussel communities from moderately wave-exposed shores tended to be dominated by crustaceans and mobile polychaetes, whereas those in more sheltered, sediment laden conditions were dominated by nemerteans and sedentary polychaetes. In both mussel species, the diversity of associated communities increased with mussel density, presumably reflecting a greater degree of environmental heterogeneity.
Bivalvia of the Buckhorn Asphalt Deposit, Late Carboniferous Boggy Formation of Oklahoma, U.S.A.

Thomas Yancey and Michael J. Heaney

Department of Geologyand Geophysics, Texas A and M University, College Station, Texas TX 77843-3115, U.S.A. E-mail: tyan@tamu.edu

Preservation of bivalve shells by sealing in asphalt at the time of deposition has retarded diagenesis and preserved many fine details not normally observed in Paleozoic bivalves. For most bivalve species, documentation is available for ontogenetic series starting with prodissoconch stages, and reveals early hinge character states, fine shell ornamentation, and original shell microstructure, as well as evidence of very early shell degradation by microboring. The Buckhorn deposit contains an abundance of small taxa, including undescribed small species. These indicate the presence of a great diversity of bivalves, especially pteriomorph bivalves, among the smaller sizes.