Text Box:     Number 52 (February 2009)
Text Box: The Malacologist

Growth and differentiation during delayed metamorphosis of feeding  gastropod larvae

Among gastropods, feeding larvae often attain larger size at metamorphosis than non-feeding larvae. Delay of metamorphosis can further influence size at recruitment if larvae continue to grow during the delay. Some caenogastopod larvae grow during delayed metamorphosis, but opisthobranch larvae do not. Larvae of the  caenogastropod Euspira lewisii and the euthyneurans Haminoea vesicula (Opisthobranchia) and Siphonaria denticulata (Pulmonata) conform to growth patterns for their respective major clades.  Furthermore, the caenogastropod continue to lengthen the prototroch (ciliary band for swimming and feeding) and to differentiate prospective post-metamorphic structures (gill filaments and radular teeth) during delayed metamorphosis. Larvae of the neritimorph Nerita atramentosa  arrested shell growth during delayed metamorphosis but the radula continued to elongate, similar to that of non-feeding larvae of the vetigastropod Haliotis. Large larval size and capacity for continued growth during delayed metamorphosis, as exhibited by some caenogastropods, appears to be a derived innovation among feeding gastropod larvae. This novelty may have facilitated post-metamorphic evolution of predatory feeding using a long proboscis.

Lesoway, Maryna P and Page, Louise Mar. Biol. 153(4) 723-734. Feb 2008.


Mortality of different life stages of marine invertebrates with planktonic larvae

The loss ratios of marine bivalves, gastropods, polychaetes and echinoderms in Danish waters from one development stage to the next, based on average abundances of pelagic larvae, benthic post-larvae and adults, gives a rough estimate of the larval and post-larval mortality. Post-larval mortality was 71.2-84.9%, and larval mortality 85.2-97.6The results confirm that the larval stage, metamorphosis and settlement are the critical phase in terms of mortality in the life cycle for Bivalvia. Assuming steady state based on actual measurements of pelagic larval densities an estimated input to the water column of pelagic bivalve larvae ranges from 10,930 to 17,157 larvae m-2 d-1 and for polychaetes between 2544 and 3994 larvae m-2 d-1. These estimates seem to correspond to the reproductive capacity of the observed adult densities using life-table values from the literature. The potential settlement of post-larvae is 43 post-larvae m-2 d-1 for Bivalvia and 56 post-larvae m-2 d-1 for Polychaeta. The adult turnover time for bivalves is estimated to be 1.5 years and for polychaetes 2.1 years. This exemplifies that species with short generation times may dominate in very dynamic transitional zones with a high frequency of catastrophic events like the frequent hypoxic events in inner Danish waters.

Pedersen, TM et al. J. Mar. Syst. 73(1-2), 185-207. Sep 2008.


Ultrasound can estimate Octopus brain size in vivo

Sonographic measurements of brain masses in vivo correlate with postmortem measurements, and brain growth is detectable when individuals are measured twice 30 days apart.

Grimaldi, AM et al. Brain Res. 1183,  66-73. 5 Dec 2007.


Molecular memory traces

This review focuses on insights gained from examining memory at the molecular level, illustrated by examples  from molecular and cellular mechanisms underlying long-term facilitation in the marine mollusc Aplysia and long-term potentiation, mainly in rodents. Particular emphasis is given to how molecular memory traces are formed and the role of protein synthesis and gene expression. Three important constraints from molecular work are (i) the induction of plasticity depends on the 'state' of the synapse; (ii) there are multiple independent molecular traces formed after experience with different half-lives; and (iii) the requirement for the conjunction of synaptic activation and new protein synthesis implies that new conjunctions are required to induce long-term memory formation.

Sossin, Wayne S. Prog. Brain Res. 170, 3-25.  2008.


Peripheral oxygen-sensing cells directly modulate the output of an identified respiratory central pattern generating neuron

Breathing is an essential homeostatic behaviour regulated by central pattern generators (CPGs). How the peripheral input modulates the activities of the respiratory CPG is unknown, partly because of the complexity of respiratory control centres in mammals. The pond snail Lymnaea stagnalis presents a simpler invertebrate model to study the basic cellular and synaptic mechanisms involved. Peripheral chemoreceptor cells (PCRCs) are identified that relay hypoxia-sensitive chemosensory information to the known respiratory CPG neuron right pedal dorsal 1. Selective perfusion of these PCRCs with hypoxic saline triggered bursting activity in these neurons and when isolated in cell culture they showed depolarization and spiking activity under hypoxia. When co-cultured with right pedal dorsal 1, the PCRCs developed synapses that exhibited a form of short-term synaptic plasticity in response to hypoxia. Finally, osphradial denervation in intact animals significantly perturbed respiratory activity compared with their sham counterparts.

Bell, Harold J et al. Eur. J. Neurosci. 25(12), 3537-3550. 2007.


First egg protein with a neurotoxic effect on mice

This is the first report of a mollusc neurotoxin genetically encoded outside the cone-snail species, in the eggs of  the freshwater apple snail Pomacea canaliculata. The neurotoxin is an oligomeric glyco-lipoprotein of 400kDa with two subunits indistinguishable from perivitellin PV2. The results of injection suggest that calcium buffering and apoptosis may play a role in the neurological disorders induced by the toxin in mammalian central nervous system.

Heras, H et al. Toxicon 52(3), 481-488. 1 Sep 2008.


Polyculture of mussels with cultured shrimp controls luminous bacterial disease

Shrimp mortality due to luminous bacteria is a problem of the shrimp industry worldwide, although polyculture of shrimp with finfish can control the growth of the bacteria. This study shows that bivalves, especially green mussel, could be used for polyculture with shrimp to control disease due to luminous bacteria. .

Tendencia, EA Aquaculture 272(1-4), 188-191. 26 Nov 2007.


Impact of invasive flatworm on arboreal snails

Field experiments on Ogasawara Islands of NW Pacific show that the snail-eating triclad Platydemus manokwari may be an important cause of the rapid decline or extinction of native arboreal snails. The flatworms tracked snail scent trails on tree trunks and ate 40% of snails in 7 days.

Sugiura S and Yamaura Y. Biological Invasions, DOI 10.1007/s10530-008-9287-1


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