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Volume 53

Systematic and Cladistic studies of the neotropical slug Omalonyx (Gastropoda, Succineidae)

Janine Arruda, Pontificia Universidade Catolica do Rio Grande do Sul, Brazil

Omalonyx d´Orbigny, 1837 are slugs with reduced, flattened and nail-shaped shell and a characteristic color pattern, with two black longitudinal stripes and blackish stains throughout their tegument and mantle (Figure 1). They live on macrophytes and adjacent vegetation in swamps and flooded areas throughout the Neotropical region (Tillier, 1981; Barker, 2001; Arruda et al., 2006; Arruda & Thomé, 2008b).

The existing literature on this species’ descriptions are generally brief and inaccurate, only containing generic information concerning the shell, the external morphology and geographical distribution (d´Orbigny, 1837; Guppy, 1872; Doering, 1874) or the radula (Heynemann, 1868; Hylton Scott & Lapuente, 1968; Hylton Scott, 1971). Detailed information on their internal anatomies are presented by Simroth (1896), Baker (1926), Patterson (1971), Tillier (1981), Arruda et. al. (2006), Arruda & Thomé (2008a,b). The only available phylogenetic proposal for this Omalonyx species was published by Tillier (1981).

My Ph. D. Project deals with a taxonomic revision and cladistic analysis of Omalonyx species. Although I had gathered specimens from several scientific collections for this study, many areas of distribution were not represented due to the lack of available specimens. Therefore, in the second half of 2008, I went on an expedition through several South American countries in order to obtain specimens from these unavailable areas, as well as to gather fresh specimens from previously explored areas. This expedition received partial financial support by the Malacological Society of London and was made in cooperation with Dr. Suzete Rodrigues Gomes (Instituto Butantan, São Paulo), who was also seeking specimens for her own project, titled “Morphological and molecular analyzes of the cryptic species of the complex Sarasinula s.l. (Mollusca, Gastropoda, Veronicellidae)”. Several researchers and institutions have cooperated with this project, providing personnel, field work transportation and laboratory facilities, as well as providing specimens and literature (Figure 2).

After researching many museum collections and gathering specimens from many localities, we were able to assemble specimens from all South American countries, as well as from the Antillean Islands of Trinidad, Dominica and Guadalupe, and the Chilean Island of Juan Fernandez. The collections under analysis pertain to the Museo de La Plata (MLP) and Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN) (Argentina), Museu de Zoologia da Universidade de São Paulo (MZUSP), Museu do Instituto Nacional de Pesquisas da Amazônia (INPA), Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul (MCT), Museu de Ciências Naturais da Fundação Zoobotânica de Porto Alegre (MCNZ) (Brazil), Museo de Historia Natural Noel Kempff Mercado (Bolivia), Muséum National d´Histoire Naturelle (MNHN) (France), Museum für naturkunde der Humboldt-Universität zu Berlin (ZMB) (Germany), Museo de Historia Natural Universidad Nacional Mayor de San Marcos (Peru), Swedish Museum of Natural History (SMNH) (Sweden), Naturhistorisches Museum Basel (NMB) (Switzerland), Museo Nacional de Historia Natural (URMU) (Uruguay), Field Museum of Natural History (FMNH), Florida Museum of Natural History (UF) (USA) and Museo de Historia Natural La Salle (MHNLS) (Venezuela). New lots from the Trinidad and Guadeloupe Islands, as well as from eastern Venezuela, were recently donated by Dr. David Robinson (USA) and Dr. Rafael Martínez ( Venezuela).

Among this expedition’s mentionable results, new specimens of O. pattersonae (Tillier, 1981) were collected at a rice farm in the Departamento de Santa Cruz de La Sierra ( Bolivia). Although this record significantly extends this species’ distribution to the south, being that its previous records only included Antigua and Venezuela, its occurrence seems to be discontinuous between said areas. Based on the collection sites and on statements from local residents, one may conclude that this species is a local rice farm plague.

The only existing record of Omalonyx in Bolivia had been made by d´Orbigny (1837), who described O. unguis (d´Orbigny, 1837). However, after this expedition, Bolivia has proven to hold the largest diversity of Omalonyx species, being that the occurrence of O. pattersonae, O. convexus (Heynemann, 1868) and O. matheroni (Potiez & Michaud, 1835) was also recorded. Therefore, this country has become the current northern distribution limit for both O. unguis and O. convexus.

Different morphotypes were found in individual collection lots from the Guadalupe and Trinidad Islands, as well as from the north and northwestern portions of South America. In some of these lots, the reproductive anatomies of the morphotypes are clearly different. Whereas, other lots presented similar morphotype anatomies, resembling the description of O. matheroni by Tillier (1981), but their reproductive organ sizes and proportions presented significant variations. According to these observations, Omalonyx matheroni could be a species complex.

Arruda & Thomé (2008b) have described sympatry between O. unguis and O. convexus from Rio Santiago, Argentina, although they are not syntopic. However, this work indicates the occurrence of syntopic morphotypes in the north and northwestern portion of South America.

For cladistic analysis purposes, each morphotype is being dissected and characterized in the matrix as a separate terminal taxon. During this process, three new species have already been discovered and their descriptions are currently in preparation.

Figure 2: Some field works and collection examination durinig the expedition: A) El Hatillo (Venezuela) with Luis Gonzalez (MHNLS) (left) and Dr. Raphael Martinez (middle); Museo do Historia Natural Universidad Nacional Mayor de San Marcos (Peru) with Dr, Rina Ramirez (behind) and Dr, Suzete Gomes (left) C) A rice farm at the Japanese colony of San Juan (Bolivia) with Yuuki (left) and Joana (CIAT) (right).


I would like to thank the Malacological Society of London for the Grant which allowed the collection of scientifically and numerically valuable material in order to support my project; Gustavo Darrigran (MLP); Alejandro Tablado (MACN); Luiz Simone (MZUSP); Célio Magalhães and Daniel Pimpão (INPA), Lúcia Richinitti (MCP); Ingrid Heydrich (MCNZ); Karina Osinaga (Museo de Historia Natural Noel Kempff Mercado); Roger Taboada and other researchers from Centro de Investigación Agrícola Tropical - CIAT (Bolivia), Yuuki Pedro Yonekura; Virginie Héros (MNHN); Matthias Glaubrecht (ZMB); Rina Ramirez and her students (Museo de Historia Natural Universidad Nacional Mayor de San Marcos); Karin Kronestedt (SMNH); Urs Wüest (NMB); Fabrizio Scarabino (URMU); Jochen Gerber (FMNH); John Slapcinsky (UF); Carlos Lasso, Alejandro Sánchez, Paula “Palito” and other researchers (MHNLS); Rafael Martínez Escarbassiere; David Robinson; Edgar Linares; Margarita Fierro and Mônica Vera for technical and scientific support as well as donated or loaned specimens; Suzete Gomes for her friendship and field support.

Cited Literature:

Arruda, J. O. & Thomé, J. W. 2008a. Synonymization of Neohyalimax with recharacterization of Omalonyx brasiliensis (Mollusca: Gastropoda: Succineidae). The Nautilus, 122 (2): 94-98.

Arruda, J. O. & Thomé, J. W. 2008b. Revalidation of Omalonyx convexus and emendation of the type locality of Omalonyx unguis (Mollusca, Gastropoda, Succineidae). Archiv für Moluskenkunde , 137 (2): 159-166.

Arruda, J. O., Gomes, S. R., Ramírez, R. & Thomé, J. W. 2006. Morfoanatomia de duas espécies do gênero Omalonyx (Mollusca, Pulmonata, Succineidae) com novo registro para Minas Gerais, Brasil. Biociências ,14(1): 61-70.

Baker, H. B. 1926. The mollusca collected by the University of Michigan – Williamson expedition in Venezuela – Part IV. Occasional Papers of the Museum of Zoology. University of Michigan, 167: 1-40, plates XII-XIX.

Barker, M. G. 2001. Gastropods on land: phylogeny, diversity and adaptive morphology. In: Barker, M. G. (Ed.). The biology of terrestrial mollusks. New York: CABI Publishing, p. 1-146.

d´Orbigny, A. 1835. Synopsis terrestrium et fluviatilium molluscorum, in suo per americam meridionalem itinere. Magasin de Zoologie, Paris, v. 5, p 1-44 [p. 2].

d´Orbigny, A. 1837. Voyage dans l’Amérique méridionale. Strasbourg, Paris, parte 3: Mollusques, v. 5, p. 185-376.

Doering, D. A. 1874. IV Apuntamientos sobre la fauna de moluscos de la Republica Argentina. Boletin de la Academia Nacional de Ciencias Exactas 1:48–77.

Guppy, R. J. L. 1872. Third series of additions to the catalogue of the land and freshwater Mollusca of Trinidad, with a revised list of all species. Proceedings of the Scientific Association of Trinidad, 2: 17-25.

Heynemann, F. D. 1868. Die Mundtheile einiger brasilianischen Land- und Süsswasserchnecken. Malakozoologische Blätler, 15 (3): 99-113.

Hylton Scott, M. I. 1971. Homalonyx weyrauchi, nueva especie de Tucuman (Gastropoda Succineidae). Neotropica, La Plata , 17 (52): 12-14.

Hylton Scott, M. I. & Lapuente, 1968. E. Valor diagnostico de la radula para especies del genero Homalonyx Orbigny. Neotropica, La Plata , 14(44): 49-56.

Patterson, C. M. 1971. Taxonomic studies of the land snail family Succineidae. Malacological Review, 4: 131-202.

Simroth, H. 1896. On Neohyalimax brasiliensis, n.gen., n.sp. (allied to Hyalimax), from Brazil. Proceedings of the Malacological Society of London, 2: 39-45.

Tillier, S. 1981. South American and Juan Fernández succineid slugs (Pulmonata). Journal of Molluscan Studies, 47: 125-146.