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Predicting the distribution of Omalonyx (Mollusca: Pulmonata: Succineidae) species from literature review, museum databases and new sampling efforts in Brazil

Predição da distribuição de Omalonyx (Mollusca: Pulmonata: Succineidae) a partir da revisão da literatura, dados de museu e novo esforço amostral no Brasil

Abstract

Accurate distributional information is crucial for studies on systematics, biodiversity and conservation. To improve the knowledge regarding the geographical distribution of Omalonyx in South America, we present updated information based on data from a literature review, institutional collections and malacological surveys. All this information composed the dataset used to predict species distribution employing the Maximum Entropy Algorithm (MaxEnt). The model was run using data on species distribution, altitude and bioclimatic variables (WorldClim database). The model had consistent performance, and areas presenting similar conditions to areas where the species were recorded were considered areas of occurrence. The predicted occurrence areas included those that were already surveyed and those that are considered potential occurrence areas. The results demonstrate that the genus has widespread distribution in the Neotropical region and occurs in the tropical, temperate and arid regions of South America and Lesser Antilles. Omalonyx spp. were recorded in all South American countries and hydrographic regions. However, in some countries, there were only isolated records (ex: Colombia and Ecuador). Here, we also present the first record of Omalonyx spp. in four Brazilian States (Acre, Rondônia, Piaui, and Amapá). The genus was found in all hydrographic regions within Brazil and among 27 federative unities; it was absent from only two unities (Roraima State and Distrito Federal). This work contributes to the knowledge on Omalonyx spp. distribution and provides an important basis for the work of ecologists and taxonomists.

Keywords:
MaxEnt; niche model; species distribution; Modeling; Succineids; Neotropic

Resumo

A informação precisa sobre a distribuição é crucial para os estudos sobre sistemática, biodiversidade e conservação. Para melhorar o conhecimento sobre a distribuição geográfica de Omalonyx na América do Sul, apresentamos informações atualizadas com base em dados de revisão de literatura, coleções institucionais e pesquisas malacológicas. Toda essa informação compôs o conjunto de dados usado para predição da distribuição de espécies empregando o Algoritmo de Entropia Máxima (MaxEnt). O modelo foi executado usando dados de distribuição de espécies, altitude e variáveis bioclimáticas (banco de dados WorldClim). O modelo apresentou um desempenho consistente e as áreas que apresentaram condições semelhantes às áreas onde as espécies foram registradas, foram consideradas áreas de ocorrência. As áreas de ocorrências previstas incluíram aquelas que já foram pesquisadas e aquelas que são consideradas áreas de ocorrência potencial. Os resultados demonstram que o gênero tem uma distribuição Neotropical ampla e que ocorre nas regiões tropical, temperada e árida da América do Sul e nas Pequenas Antilhas. Omalonyx spp. foram registradas em todos os países e bacias sul-americanas. No entanto, em alguns países, apenas registros isolados foram encontrados (ex: Colômbia e Equador). Aqui, também apresentamos o primeiro registro de Omalonyx spp. em quatro estados brasileiros (Acre, Rondônia, Piauí e Amapá). O gênero foi encontrado em todas as regiões hidrográficas no Brasil e nas 27 unidades federativas; sendo ausente em apenas duas unidades federativas (Estado de Roraima e Distrito Federal). Esse trabalho contribui para o conhecimento da distribuição das espécies de Omalonyx e fornece uma importante base para trabalhos de ecólogos e taxonomistas.

Palavras chave:
MaxEnt; modelagem de nichos; distribuição de espécies; Modelagem; Succineídeos; Neotrópico

Introduction

The genus Omalonyxd’Orbigny, 1837D`ORBIGNY, A. 1837. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3. P. Bertrand, Paris, France. presents a reduced shell and represents one of the slug-like lineages within the family Succineidae (Patterson 1971PATTERSON, C.M. 1971. Taxonomic studies of the land snail family Succineidae. Malacol. Rev. 4:131-202., Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Barker 2001BARKER, M.G. 2001. Gastropods on land: phylogeny, diversity and adaptive morphology. In The biology of terrestrial mollusks (M.G. Barker, ed.). CABI Publishing, New York, USA, p. 1-146.). The earliest fossil records of Succineidae were from the Tertiary of Europe and, currently, most of the diversity within the family occurs in the islands of the Pacific, in the Indian subcontinent and the Americas (Barker 2001BARKER, M.G. 2001. Gastropods on land: phylogeny, diversity and adaptive morphology. In The biology of terrestrial mollusks (M.G. Barker, ed.). CABI Publishing, New York, USA, p. 1-146.). These Neotropical slugs are terrestrial, live on aquatic macrophytes or riparian vegetation and can also be found in humid soil (Garcia et al. 2012GARCIA, M.V.B., ARRUDA, J.O., PIMPÃO, D.M. & GARCIA, T.B. 2012. Ocorrência e controle de lesmas do gênero Omalonyx (Gastropoda, Succineidae), pragas de capim-elefante Pennisetum purpureum (Poaceae) em Rio Preto da Eva, Amazonas. Acta Amaz. 42(2):227-230.). They can act as agricultural plagues (Olazarri 1979OLAZARRI, J. 1979. Los Moluscos plaga de los cultivos de “berro” en Salto, Uruguay. Comun. Soc. Malacol. Urug. 5: 63-69., Garcia et al. 2012GARCIA, M.V.B., ARRUDA, J.O., PIMPÃO, D.M. & GARCIA, T.B. 2012. Ocorrência e controle de lesmas do gênero Omalonyx (Gastropoda, Succineidae), pragas de capim-elefante Pennisetum purpureum (Poaceae) em Rio Preto da Eva, Amazonas. Acta Amaz. 42(2):227-230.) and are agents in the control of water-cress (Poi de Neiff et al. 1977POI DE NEIFF, A., NEIFF, J.J. & BONETTO, A. 1977. Enemigos naturales de Eichhornia crassipes en el nordeste argentino y posibilidades de su aplicación el control biológico. Ecosur. 4:137-156.). They can also act as intermediate hosts of an avian trematode, Leucochloridium (Lutz 1921LUTZ, A. 1921. Obervações sobre o gênero Urogonimus e uma nova forma de Leucochloridium em novo hospedador. Mem. Inst. Oswaldo Cruz. 13:136-140., Travassos 1928TRAVASSOS, L.1928. Fauna helminthológica de Mato Grosso. Trematódeos – Parte I. Mem. Inst. Oswaldo Cruz 21:309-741.), in the wild and of the nematodes Angiostrongylus costaricensis and A. vasorum in the laboratory (Montresor et al. 2008MONTRESOR, L.C., VIDIGAL, T.H.D.A., MENDONÇA, C.L.G.F., FERNANDES, A.A., DE SOUZA, K.N., CARVALHO, O.S., CAPUTO, L.F.G., MOTA, E.M. & LENZI H.L. 2008. Angiostrongylus costaricensis (Nematoda: Protostrongylidae): migration rote in experimental infection of Omalonyx sp. (Gastropoda: Succineidae). Paras. Res. 103:1339-1346., Mozzer et al. 2011MOZZER, L.R., MONTRESOR, L.C., VIDIGAL, T.H.D.A. & LIMA, W.S. 2011. Angiostrongylus vasorum: Experimental infection and larval development in Omalonyx matheroni. J. Parasitol. Res. 2011:1-4).

Currently, it is assumed that the genus comprises six recognized species (Tillier 1980TILLIER, S. 1980. Gastéropodes terrestres et fluviatiles de Guyane française. Mém. Mus. Natl. Hist. Nat., Ser. A 118:1-188., 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Martínez 1993, Arruda & Thomé 2008aARRUDA, J.O. & THOMÉ, J.W. 2008a. Synonymization of Neohyalimax, Simroth, 1896 and Omalonyx d’Orbigny, 1837, with redescription of Omalonyx brasiliensis (Simroth, 1896) (Gastropoda: Succineidae). The Nautilus 122:96-98., bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166., Arruda et al. 2009ARRUDA, J.O., PEREIRA, D., BERGONCI, P.E.A., SANTOS, C.P. & MANSUR, M.C.D. 2009. Novos registros de Omalonyx matheroni (Potiez & Michaud, 1835) (Mollusca: Gastropoda: Succineidae) para os Estados de São Paulo e Paraná, Brasil. Biotemas. 22:187-190., Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.): Omalonyx convexus (Martens, 1868MARTENS, E.V. 1868. Ueber südbrasilische Land und Süsswasser mollusken. Malakozool. Blätter. 15:169-217.), Omalonyx unguis (d’Orbigny, 1837D`ORBIGNY, A. 1837. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3. P. Bertrand, Paris, France.), Omalonyx brasiliensis (Simroth, 1896SIMROTH, H. 1896. On Neohyalimax brasiliensis, n. gen., n. sp. (allied to Hyalimax), from Brazil. Proc. Malacol. Soc. Lond. 2:39-45.), Omalonyx matheroni (Pontiez & Michaud, 1835), Omalonyx geayi Tillier, 1980, and Omalonyx pattersonae Tillier, 1981. However, identification of the species within this genus is greatly complicated by intraspecific morphological variation in the diagnostic characteristics such as the papillae on the internal surface of the penis, the insertion of the retractor muscle of the penis, the shape of papillae on the inner surface of the vagina and others (Tillier 1980TILLIER, S. 1980. Gastéropodes terrestres et fluviatiles de Guyane française. Mém. Mus. Natl. Hist. Nat., Ser. A 118:1-188., 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Martínez 1993, Arruda & Thomé 2008aARRUDA, J.O. & THOMÉ, J.W. 2008a. Synonymization of Neohyalimax, Simroth, 1896 and Omalonyx d’Orbigny, 1837, with redescription of Omalonyx brasiliensis (Simroth, 1896) (Gastropoda: Succineidae). The Nautilus 122:96-98., bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166., Arruda et al. 2009ARRUDA, J.O., PEREIRA, D., BERGONCI, P.E.A., SANTOS, C.P. & MANSUR, M.C.D. 2009. Novos registros de Omalonyx matheroni (Potiez & Michaud, 1835) (Mollusca: Gastropoda: Succineidae) para os Estados de São Paulo e Paraná, Brasil. Biotemas. 22:187-190., Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.).

To improve taxonomic knowledge on Omalonyx species, studies encompassing morphological and molecular data are essential. However, the first step to elucidating these questions is to acquire knowledge on species geographical distribution. Accurate geographical distributional information is crucial to solve systematics and biogeographic problems and to drive conservation efforts. Species-distribution models infer potential distribution from data on observed distribution and from environmental variables related to the sites where occurrences were recorded (Bradie & Leung 2017BRADIE, J. & LEUNG, B. 2017. A quantitative synthesis of the importance of variables used in MaxEnt species distribution models. J. Biogeogr. 44:1344-1361.). These models assume that climate ultimately restricts a species' distribution and summarize it with a number of climatic variables within the known range of the species, generating a bioclimatic profile. They play an important role as first filters in assessing the potential distribution of each species, improving the success of future sampling efforts and providing initial insight into the bioclimatic tolerance of different species (Beaumont et al. 2005BEAUMONT, L.J., HUGHES, L. & POULSEN, M. 2005. Predicting species distributions: use of climatic parameters in BIOCLIM and its impact on predictions of species’ current and future distributions. Ecol. Model. 186:250-269., Rubio & Acosta 2011RUBIO, G.D. & ACOSTA, L.E. 2011. Geographical distribution of the space-weaving spider, Chibchea salta, from northwestern Argentina: New records and bioclimatic modeling. J. Insect Sci. 11:54.). These tools have also been applied in several conservation biology studies to identify areas with high species richness and to predict effects of climate change on species’ distributions (Araújo & Rahbek 2006ARAÚJO, M.B. & RAHBEK, C. 2006. How does climate change affect biodiversity? Science. 313:1396-1397., Costa et al. 2010COSTA, G.C., NOGUEIRA. C., MACHADO, R.B. & COLLI, G.R. 2010. Sampling bias and the use of ecological niche modeling in conservation planning: a field evaluation in a biodiversity hotspot. Biodivers. Conserv. 19:883-899., Vogler et al. 2013VOGLER, R. E., BELTRAMINO A. A., SEDE, M. M., GUTIÉRREZ GREGORIC, D. E., NÚÑEZ, V. & RUMI, A. 2013. The giant african snail, Achatina fulica (Gastropoda: Achatinidae): Using bioclimatic models to identify South American areas susceptible to invasion. Am. Malacol. Bull. 31(1):39-50.).

There are several methods to model species distribution, and they may use presence/absence, abundance or presence-only data. Usually, species records have limited coverage and consist of presence-only data (Elith et al. 2011ELITH, J., PHILLIPS, S.J., HASTIE, T., DUDÍK, M., CHEE, Y.E. & YATES, C.J. 2011. A statistical explanation of MaxEnt for ecologists. Divers. Distrib. 17(1):43-57.). The Maximum Entropy Algorithm (MaxEnt) presents high performance for modeling presence-only data and is widely used to model species distribution (Bradie & Leung 2017BRADIE, J. & LEUNG, B. 2017. A quantitative synthesis of the importance of variables used in MaxEnt species distribution models. J. Biogeogr. 44:1344-1361.). Here, we use this method to improve the knowledge on the geographical distribution of Omalonyx spp., assembling literature data with specimens either collected in our surveys, from malacological collections or donated by partner laboratories. These data on species presence and the associated bioclimatic variables were used to model species distribution, to investigate the main environmental factors related to the occurrence of Omalonyx species and to detect species with overlapping distribution areas. This work improves the knowledge on these slugs' distribution, providing information to propel advances in the morphological and molecular taxonomy of these neotropical succineids.

Material and Methods

Literature data on Omalonyx was reviewed (until December 2016) in order to find records of its occurrence across the Neotropical region (see the topic literature review in the results). Institutions harboring preserved specimens were identified in the literature review and by onsite and virtual searching in institutional collections (Table 1), and information regarding the lot number and collection site was organized in two tables (Table 2 and 3). Donated specimens were also included in these tables (Table 2 and 3).

Table 1
Institutions harbouring specimens of Omalonyx found after literature review, visits and virtual search in collections databases.
Table 2
Records of Omalonyx in Brazil based on literature data, institutional collections, and our own malacological surveys.
Table 3
Records of Omalonyx in South America and Lesser Antilles based on literature data, institutional collections and our own malacological surveys.

To investigate in detail the distribution of these slugs in Brazil, malacological surveys comprising all geographical regions (North, Northeast, Southeast, South and Central West) were conducted between 2006 and 2016 (permission from environmental agency: ICMBio/SISBIO no. 12113-3). Specimens were manually collected from wet soil and vegetation in the vicinity of freshwater systems. Voucher specimens were deposited in the malacological collection of the Laboratório de Malacologia e Sistemática Molecular (LMSM), at Universidade Federal de Minas Gerais, Minas Gerais, Brazil.

All localities from the literature review, museums, collections, donations and our own malacological surveys were listed (Table 2 and 3) and plotted on a map (Figure 1) using the software ArcGIS 10.4 (ArcGIS Desktop 10.4 Geostatistical Analyst, Environmental Systems Research Institute ESRI, 2016). The geographic position of the localities and the information about South American hydrography and geography were cross-checked with Google Earth, Global Gazetteer, Hydro web (a hydrologic information system of Agência Nacional de Águas - ANA, the national water resources agency of the Environment Ministry, Brazil). Information regarding the hydrography of Austral South America was obtained from Bonetto (1994)BONETTO, A.A. 1994. Austral rivers of South America. In Limnology now: a paradigm of planetary problems (Margaleff R. ed.). Elsevier Science, Amsterdam, n. 17, p. 425-472..

Figure 1
Updated distribution of the genus Omalonyx across Neotropical region. The coloured areas represent different hydrographic regions and their respective numbers. The solid black line indicates the borders among South American countries and within Brazilian administrative regions. The species records were represented by colours dots: red = O. matheroni; blue = O. convexus; green = O. unguis; yellow = O. geayi, purple = O. pattersonae, black = O. brasiliensis; gray = do not identified until species level, or Omalonyx sp. and gray circle with black border = Specimens from Chile that were previously identified as O. gayana. The stars represents the records made in our surveys, the circles represents literature or museums data and the cross symbol represents the samples that were donated by other researchers. Details about each sample are on tables 2 and 3. Hydrographic regions are indicated by numbers: 1) Pacific Coast; 2) Caribbean sea; 3) Orinoco River; 4) Amapá-Esequibo; 5) Amazon River; 6) Tocantins River; 7) North Atlantic; 8) São Francisco River; 9) Eastern Atlantic; 10) Del Plata; 11) Border strip of the Brasilica (North) and the Chilean‑Patagonian (South West) Subregion; 12) Eastern; 13) Chilean-Patagonian Subregion of the Pacific Versant; 14) Chilean-Patagonian Subregion of the Atlantic Versant.

Morphological identification of specimens collected in our malacological surveys was based on characteristics of the reproductive system according to the following literature: O. convexus (Hylton-Scott & Lapuente 1968HYLTON-SCOTT, M.I. & LAPUENTE, E. 1968. Valor diagnostico de la Radula para especies del genero Omalonyx Orbigny. Neotropica 14:49-56., Hylton-Scott 1971HYLTON-SCOTT, M.I. 1971. Homalonyx weyrauchi, Nueva especie de Tucuman. Neotropica. 17:12-14., Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Arruda & Thomé 2008bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.), O. unguis (Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.), O. matheroni, O. pattersonae and O. geayi (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.). Specific identification provided in the papers (literature review) and on the labels (museum specimens) was also used in this work. Some of these records were not identified to species level and are designated Omalonyx sp. Until 1981, there were several species of Omalonyx, now recognized as synonyms. Throughout the text, species are designated according to Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. and Arruda & Thomé (2008aARRUDA, J.O. & THOMÉ, J.W. 2008a. Synonymization of Neohyalimax, Simroth, 1896 and Omalonyx d’Orbigny, 1837, with redescription of Omalonyx brasiliensis (Simroth, 1896) (Gastropoda: Succineidae). The Nautilus 122:96-98., bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.), where synonyms for the six valid Omalonyx species can be found. However, when consulting the topic references, the reader will find the former designation.

Data of occurrence (Table 2 and 3) were used to model the species geographic distributions using one topographic variable (altitude) and the nineteen bioclimatic variables derived from the WorldClim database v. 1.4 as showed by Vogler et al. (2013)VOGLER, R. E., BELTRAMINO A. A., SEDE, M. M., GUTIÉRREZ GREGORIC, D. E., NÚÑEZ, V. & RUMI, A. 2013. The giant african snail, Achatina fulica (Gastropoda: Achatinidae): Using bioclimatic models to identify South American areas susceptible to invasion. Am. Malacol. Bull. 31(1):39-50. (Table 4). The classifications of climate were based on Koppen-Geiger climate classification types for South America (Peel et al. 2007PEEL, M.C., FINLAYSON, B.L. & MCMAHON, T.A. 2007. Updated world map of the Koppen-Geiger climate classification. Hydrol. Earth Syst. Sci. Discuss. 4:439-473.). Maps for the distribution of O. matheroni, O. pattersonae, O. geayi, O. convexus and O. unguis were produced.

Table 4
Bioclimatic variables used in models development.

To minimize the spatial autocorrelation of the bioclimatic variables and to determine which variables contributed more to the development of the model, a principal component analysis (PCA) was carried out in the areas of Omalonyx species occurrence. The resulting rasters were used to generate a potential distribution model for South America. The input parameters followed the MaxEnt (version 3.3.3k) (Phillips et al. 2004PHILLIPS, S.J., DUDIK, M. & SCHAPIRE, R.E. 2004. A maximum entropy approach to species distribution modeling. In Proceedings of the Twenty-First International Conference on Machine Learning (C. Brodley coord.). Banff, Alberta, Canada, p. 655-662.) default options except for the threshold rule, which was set as “minimum training presence”. The resulting models were processed and reclassified using ArcGIS. A binary map (absence-presence) for the potential distribution of a species was generated considering the average map that represents the induced and adjusted habitat of each species.

Results

1. Literature review

Inferences on the distribution of Omalonyx species have been made since its description, and it was assumed to be throughout South America east of the Andes (d’Orbigny 1837D`ORBIGNY, A. 1837. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3. P. Bertrand, Paris, France.). This first inference was based on records from Bolivia and Paraguay (d’Orbigny 1835aD’ORBIGNY, A. 1835a. Synopsis terrestrium et fluviatilum molluscorum, in suo per americam meridionalem itinere, ab A. d’Orbigny, collectorum. Mag. Zool. 5:1-44., 1837). However, at that time (1837), the name Omalonyx was used as the subgenus Succinea (Omalonyx) unguis. Later, Omalonyx was used at the genus level (Herrmannsen 1849HERRMANNSEN, N.A. 1849. Indicis generum malacozoorum primorida. v.2. Theodore Fischer, Cassells, Ortmann, Berlin.). In addition to the publications of d’Orbigny other species were described at that time as showed below. In the next century, Patterson (1971)PATTERSON, C.M. 1971. Taxonomic studies of the land snail family Succineidae. Malacol. Rev. 4:131-202. extended the distribution of the genus to several West Indies islands and Central America. However, the basis for this conclusion was not clearly demonstrated. After that, Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. demonstrated the occurrence of Omalonyx species in all South America east of the Andes and the Lesser Antilles. His conclusion was based on preserved specimens from malacological collections that did not include significant sampling material from Brazil, although there were already records on the presence of Omalonyx spp. in the country years before (e.g., Moricand 1836MORICAND, S. 1836. Troisième supplément au mémoire sur les coquilles terrestres et fluviates de la Province de Bahia. Sociétéde Physique et d’Historie naturelle de Genève, Genébra, 7:415-446., Gibbons 1879GIBBONS, J.S. 1879. Comparison of Omalonyx unguis, D’Orb. with O. felina, Guppy. J. Conchol. 2:99-101.). In fact, Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. studied animals from only eight localities in Brazil, and four of these could not be clearly located and were excluded from his study. In this work, Tillier also discusses the origin and evolution of South American and Juan Fernandéz Islands (Chile) succineids. He suggests that the southeast region of Brazil is the center of Omalonyx radiation once three species can be found in this region (O. unguis, O. matheroni and O. brasiliensis). Details on the records of Omalonyx occurrence in the Neotropics are given below in the subsections “Omalonyx in Brazil” and “Omalonyx in other South American countries and Lesser Antilles”.

1.1. Literature review: Omalonyx in Brazil

The first record of Omalonyx in Brazil was made in the 19th century in the Northeastern region (Moricand 1836MORICAND, S. 1836. Troisième supplément au mémoire sur les coquilles terrestres et fluviates de la Province de Bahia. Sociétéde Physique et d’Historie naturelle de Genève, Genébra, 7:415-446.) on a lake in Bahia State named “la Digue” or “le Baril”. The specimens were identified as O. unguis. Hidalgo (1869)HIDALGO, J.G. 1869. Moluscos del viaje al pacífico verificado de 1862 á 1865 por una comisión de naturalistas enviada por el gobierno español. Parte primera, Univalvos terrestres. Imprenta de Miguel Ginesta, Madrid, Spain. also identified as O. unguis specimens collected by Paz and Martinez in Bahia State. Two years later, the same author (Hidalgo 1872HIDALGO, J.G. 1872. Moluscos del viaje al pacífico verificado de 1862 a 1865 por uma comision de naturalistas enviada por el gobierno español. Parte primera, Univalvol terrestres. Madrid: Imprenta de Miguel Ginesta.) stated that Paz and Martinez collected those specimens at “Lago Dique” (Dike Lake), Salvador, Bahia. We suppose that the specimens cited by Moricand (1836)MORICAND, S. 1836. Troisième supplément au mémoire sur les coquilles terrestres et fluviates de la Province de Bahia. Sociétéde Physique et d’Historie naturelle de Genève, Genébra, 7:415-446. and Hidalgo (1869HIDALGO, J.G. 1869. Moluscos del viaje al pacífico verificado de 1862 á 1865 por una comisión de naturalistas enviada por el gobierno español. Parte primera, Univalvos terrestres. Imprenta de Miguel Ginesta, Madrid, Spain., 1870HIDALGO, J.G. 1870. Catalogue des coquilles terrestres recueillies par naturalistes de la commission scientifique espagnole sur divers points de l’Amérique méridionale. J. Conchol. 18:27-70.) were collected in an urban lake known since the colonial period as “Dique do Tororó”. Gibbons (1879)GIBBONS, J.S. 1879. Comparison of Omalonyx unguis, D’Orb. with O. felina, Guppy. J. Conchol. 2:99-101. identified two different species of Omalonyx in Bahia State, O. unguis and O. matheroni. However, no other information about the locality was provided, and the morphology described in Gibbons (1879)GIBBONS, J.S. 1879. Comparison of Omalonyx unguis, D’Orb. with O. felina, Guppy. J. Conchol. 2:99-101. is not compatible with O. unguis; thus these records were not included in Table 2. Omalonyx convexus was described by Martens (1968) as Succinea convexa from specimens collected in Porto Alegre, Rio Grande do Sul State, in southern Brazil (type locality), and it was later included in the genus Omalonyx (Arruda & Thomé 2008bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.). The map provided by Arruda and Thomé (2008b)ARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166. shows overlapping distribution of O. convexus and O. unguis in the Argentinean region of the Paraná River basin (in Figure 1 the Paraná River basin is included in the Del Plata hydrographic region) and adjacent localities in Uruguay. Omalonyx brasiliensis was described by Simroth (1896)SIMROTH, H. 1896. On Neohyalimax brasiliensis, n. gen., n. sp. (allied to Hyalimax), from Brazil. Proc. Malacol. Soc. Lond. 2:39-45. based on specimens collected by H. von Ihering in Rio Grande do Sul State.

In the 20th century, specimens of Omalonyx infected by Leucochloridium, an avian trematode, were found by Lutz (1921)LUTZ, A. 1921. Obervações sobre o gênero Urogonimus e uma nova forma de Leucochloridium em novo hospedador. Mem. Inst. Oswaldo Cruz. 13:136-140. in the surroundings of the institute where he used to work in Rio de Janeiro city, Rio de Janeiro State. The author also reported that this slug is abundant in the north of Brazil. This trematode was also found in birds from Mato Grosso and used in the experimental infection of Omalonyx (Travassos 1928TRAVASSOS, L.1928. Fauna helminthológica de Mato Grosso. Trematódeos – Parte I. Mem. Inst. Oswaldo Cruz 21:309-741.). Both of these works have a parasitological focus, and the specific identification of the slug was not provided. Haas (1939)HAAS, F. 1939. Zur Kenntnis der Binnen-Mollusken NO - Brasiliens. Senckenb. Biol. 21:254-278. registered O. unguis for the State of Pernambuco but did not specify the locality. Parodiz (1957)PARODIZ, J.J. 1957. Catalogue of the land Mollusca of Argentina. The Nautilus. 70:127-135. recorded O. unguis in Brazil but did not include the locality. He also mentioned the occurrence of O. unguis in Porto Alegre (Rio Grande do Sul State) and observed its similarity to O. convexus. Based on specimens from the MCZ (lot number unavailable), Parodiz (1963)PARODIZ, J.J. 1963. Observaciones anatomicas sobre Omalonyx patera Doer., com una nota biografica acerca de Adolfo Doering (1848-1926). Sterkiana. 12:1-7. registered the occurrence of Omalonyx in Rio de Janeiro (O. unguis) and Camaquã, Rio Grande do Sul. The specimens from Camaquã were later identified as O. convexus (Arruda & Thomé 2008bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.). Lange de Morretes (1949)LANGE DE MORRETES, F. 1949. Ensaio de Catálogo dos Moluscos do Brasil. Arq. Mus. Para. 7:1-216. recorded O. brasiliensis and O. unguis in Vila Nova (Bahia State) and O. matheroni in Santarém (Pará State). In a taxonomical review using specimens from institutional collections, Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. studied animals from eight localities in Brazil. Three of them were easily identified: Santarém and Alenquer in Pará State, and Rio de Janeiro in Rio de Janeiro State. The other four localities, due to insufficient labeling information, could not be precisely located. Two of them were only superficially specified: “Brazil” Pernambuco State and Praya (=Praia) Grande (Rio de Janeiro State). The other two localities could not be identified: Santa Amélia, Amazonas and “Makthlawara” (BMNH 1929.10.2.6.22). This author also mentioned the occurrence of Omalonyx in Porto Alegre, Rio Grande do Sul State, and cited Martens (1868)MARTENS, E.V. 1868. Ueber südbrasilische Land und Süsswasser mollusken. Malakozool. Blätter. 15:169-217. and Simroth (1896)SIMROTH, H. 1896. On Neohyalimax brasiliensis, n. gen., n. sp. (allied to Hyalimax), from Brazil. Proc. Malacol. Soc. Lond. 2:39-45., who also recorded O. brasiliensis in this State (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.). The distribution of Omalonyx in Brazil was revisited by two authors whose results were similar to those of Lange de Morretes (1949)LANGE DE MORRETES, F. 1949. Ensaio de Catálogo dos Moluscos do Brasil. Arq. Mus. Para. 7:1-216.. First, Salgado & Coelho (2003)SALGADO N.C. & COELHO. A.C.S. 2003. Moluscos terrestres do Brasil (Gastrópodes operculados ou não, exclusive Veronicellidae, Milacidae e Limacidae). Rev. Bio. Trop. 51:149-189. reported some species of the genus in a review about Brazilian land snails but did not cite any locality. After that, Simone (2006)SIMONE, L.R.L. 2006. Land and Freshwater molluscs of Brazil. EGB, Fapesp, São Paulo. cited the occurrence of O. brasiliensis in Rio Grande do Sul State and considered the occurrence area for the genus Omalonyx to be from Bolivia to Patagonia. Several other records were made in Brazil, including Minas Gerais (Oliveira & Almeida 2000OLIVEIRA, M.P. & ALMEIDA, M.N. 2000. Inventário preliminar dos Moluscos do Estado de Minas Gerais, Brasil. Strombus. 6:01-06., Arruda et al. 2006ARRUDA, 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. 14:61-70., Montresor et al. 2008MONTRESOR, L.C., VIDIGAL, T.H.D.A., MENDONÇA, C.L.G.F., FERNANDES, A.A., DE SOUZA, K.N., CARVALHO, O.S., CAPUTO, L.F.G., MOTA, E.M. & LENZI H.L. 2008. Angiostrongylus costaricensis (Nematoda: Protostrongylidae): migration rote in experimental infection of Omalonyx sp. (Gastropoda: Succineidae). Paras. Res. 103:1339-1346.) and São Paulo State (Arruda et al. 2009ARRUDA, J.O., PEREIRA, D., BERGONCI, P.E.A., SANTOS, C.P. & MANSUR, M.C.D. 2009. Novos registros de Omalonyx matheroni (Potiez & Michaud, 1835) (Mollusca: Gastropoda: Succineidae) para os Estados de São Paulo e Paraná, Brasil. Biotemas. 22:187-190., Eduardo et al. 2012EDUARDO, J.M., TAKAHASHI, F.Y., HOLCMAN, M.M., DA COSTA, C.B.T.L. & OHLWEILER, F. 2012. Freshwater gastropods and helminthes associated, in water collections from Santo André, São Paulo, Brazil. Biociências. 18:22-34.) in the southeast; Paraná (Arruda et al. 2009ARRUDA, J.O., PEREIRA, D., BERGONCI, P.E.A., SANTOS, C.P. & MANSUR, M.C.D. 2009. Novos registros de Omalonyx matheroni (Potiez & Michaud, 1835) (Mollusca: Gastropoda: Succineidae) para os Estados de São Paulo e Paraná, Brasil. Biotemas. 22:187-190., Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.), Rio Grande do Sul (Arruda & Thomé 2008aARRUDA, J.O. & THOMÉ, J.W. 2008a. Synonymization of Neohyalimax, Simroth, 1896 and Omalonyx d’Orbigny, 1837, with redescription of Omalonyx brasiliensis (Simroth, 1896) (Gastropoda: Succineidae). The Nautilus 122:96-98., bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166., Arruda & Thomé 2011ARRUDA, J.O. & THOMÉ, J.W. 2011. Biological aspects of Omalonyx convexus (Mollusca, Gastropoda, Succineidae) from the Rio Grande do Sul State, Brazil. Biotemas. 24 (4):95-101., Maltchik et al. 2010MALTCHIK, L., STENERT, C. KOTZIAN, C.B. & PEREIRA, D. 2010. Responses of freshwater molluscs to environmental factors in Southern Brazil wetlands. Braz. J. Biol. 70(3):473-482.) and Santa Catarina State (Agudo-Padron 2008AGUDO-PADRON, A.I. 2008. Listagem sistemática dos moluscos continentais ocorrentes no Estado de Santa Catarina, Brasil. Comun. Soc. Malacol. Urug. 9(91):147-179., 2012AGUDO-PADRON, A.I. 2012. Nuevos aportes a la lista sistemática de moluscos continentales ocurrentes en el Estado de Santa Catarina, Brasil. Amici Molluscarum. 20(1):35-42.) in the south; Mato Grosso and Mato Grosso do Sul State (Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.) in the central west; Pernambuco (Dutra-Clarke et al. 2001DUTRA-CLARKE, A.V.C., WILLIAMS, C., DICKSTEIN, R., KAUFER, N. & SPOTILA, J.R. 2001. Inferences on the phylogenetic relationships of Succineidae (Mollusca, Pulmonata) based on 18S rRNA gene. Malacologia. 43:223-236.), Sergipe (Jesus & Manso, 2010JESUS, L.S. & MANSO, C. L.C. 2010. Inventário da coleção de referência de moluscos terrestres e límnicos do LABIMAR, Campus Prof. Alberto Carvalho da Universidade Federal de Sergipe. Scientia Plena. 6(12):121001.) and Maranhão State (Cantanhede et al. 2014CANTANHEDE, S.P.D., FERNANDEZ, M.A., MATTOS, A.C., MONTRESOR, L.C., SILVA-SOUZA, N. & THIENGO, S.C. 2014. Freshwater gastropods of the Baixada Maranhense Microregion, an endemic area for schistosomiasis in the State of Maranhão, Brazil: I - qualitative study. Rev. Soc. Bras. Med. Trop. 47:79-85.) in the northeast; and Amazonas State in the North (Pimpão 2007PIMPÃO, D.M. 2007. Moluscos. In Biodiversidade do médio rio Madeira: bases científicas para propostas de conservação (L.H. Rapp Py-Daniel, C.P. Deus, A.L. Henriques, D.M. Pimpão, O.M. Ribeiro eds). INPA/MMA/MCT Manaus, Brazil, p. 69-81, Garcia et al. 2012GARCIA, M.V.B., ARRUDA, J.O., PIMPÃO, D.M. & GARCIA, T.B. 2012. Ocorrência e controle de lesmas do gênero Omalonyx (Gastropoda, Succineidae), pragas de capim-elefante Pennisetum purpureum (Poaceae) em Rio Preto da Eva, Amazonas. Acta Amaz. 42(2):227-230.). Coscarelli & Vidigal (2011)COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403. investigated the distribution of O. unguis in Brazil and included new records for this species. Recently, new records for O. geayi extended the distribution range of this species in northern South America including Brazil (Arruda et al. 2016ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019.). The presence of Omalonyx was recorded in several Brazilian States representing all geographic regions (Table 2). All data and details (i.e., species and coordinates) on species distribution in Brazil were included in Table 2 and are shown in Figure 1.

1.2. Literature review: Omalonyx in other South American countries and Lesser Antilles

Several South American and Lesser Antilles countries are included in the distribution area of the genus Omalonyx (Figure 1, Table 3). The occurrence of O. unguis in Paraguay and Bolivia was reported by d’Orbigny (1835aD’ORBIGNY, A. 1835a. Synopsis terrestrium et fluviatilum molluscorum, in suo per americam meridionalem itinere, ab A. d’Orbigny, collectorum. Mag. Zool. 5:1-44., bD’ORBIGNY, A. 1835b. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3 – Planches. P. Bertrand, Paris, France., 1837). On this occasion, the author did a complete textual description of the external appearance of the animal and specified the collection sites: the flooded margins of Paraná River, near Corrientes, and the swamps of Moxos Province in Bolivia. Corrientes is a city on the riverbank of the Paraná River in Argentina, very close to the frontier with Paraguay, which is defined by the Paraná River itself. Later, Asunción, in Paraguay, was considered to be the type locality for O. unguis (Arruda & Thomé 2008bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.).

Omalonyx matheroni was described from individuals collected in Guadeloupe, Lesser Antilles (Potiez & Michaud 1835POTIEZ, V.L.V. & MICHAUD, A.L.G. 1835. Galerie des Mollusques, ou catalogue méthodique, descriptif et raisonné, de mollusques et coquilles du muséum de Douai. J.B. Baillière, Paris, France.). Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. studied specimens he collected or borrowed from institutional collections that were from several localities including the Lesser Antilles, Guiana, Suriname, French Guyana, Ecuador, Paraguay, Argentina and Peru (Table 3). Omalonyx occurrence in South American countries has been well documented by several authors: Argentina (Arruda & Thomé 2008aARRUDA, J.O. & THOMÉ, J.W. 2008a. Synonymization of Neohyalimax, Simroth, 1896 and Omalonyx d’Orbigny, 1837, with redescription of Omalonyx brasiliensis (Simroth, 1896) (Gastropoda: Succineidae). The Nautilus 122:96-98., bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166.); Brazil (see above the topic geographic distribution of Omalonyx in Brazil); Colombia (Vera-Ardila 2008VERA-ARDILA, M. L. 2008. Lista de los géneros de moluscos terrestres de Colombia (Mollusca: Gastropoda: Prosobranchia: Mesogastropoda y Pulmonata: Stylommatophora). Biota Colombiana. 9:39-62.); Uruguay (Olazarri 1979OLAZARRI, J. 1979. Los Moluscos plaga de los cultivos de “berro” en Salto, Uruguay. Comun. Soc. Malacol. Urug. 5: 63-69., Scarabino 2003SCARABINO, F. 2003. Lista sistemática de los Gastropoda terrestres vivientes de Uruguay. Comun. Soc. Malacol. Urug. 8:203-214., Arruda & Thomé 2008bARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166..); French Guiana (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Arruda et al. 2016ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019.); Ecuador (Hermann & Dundee 1967HERMANN, P.W. & DUNDEE, D.S. 1967. Notes on Omalonyx. Sterkiana. 28:1-6., Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Arruda et al. 2016ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019.); Suriname (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Arruda et al. 2016ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019.) Venezuela (Martens 1873MARTENS, E.V. 1873. Die Binnenmollusken Venezuela’s. In Festschrift zur Feier des hundertjahrigen Bestehens der Gesellschaft naturforschender Freunde zu Berlin (Ferd. D. Verlagsbuchhandlung ed.). Harrwitz & Grossmann, Berlin, Germany, p.157-225., Baker 1925BAKER, H.B. 1925. The Mollusca collected by the University of Michigan-Williamson Expedition in Venezuela, Part III: Pupillidae to Oleacinidae. Occas. Pap. Mus. Zool. Univ. Mich. 156:1-56., 1926BAKER, H.B. 1926. The Mollusca collected by the University of Michigan-Williamson Expedition in Venezuela, Part IV. Occas. Pap. Mus. Zool. Univ. Mich. 157:1-65., Escarbassiere 1993ESCARBASSIERE, R.M. 1993. Nota acerca de la presencia de la babosa Omalonyx (O.) pattersonae Tillier, 1981 (Gastropoda-Pulmonata Succineidae) en Venezuela. Acta Biol. Venez. 14:65-69.); Guyana (Gibbons 1879GIBBONS, J.S. 1879. Comparison of Omalonyx unguis, D’Orb. with O. felina, Guppy. J. Conchol. 2:99-101., Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.); Peru (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Ramirez, 1991RAMIRES, R. 1991. Primer registro de los géneros Adelopoma Doering, 1884, Ceciloides Férussac, 1814, Pupisoma Stoliczka, 1873 y Omalonyx D`Òrbigny, 1841 (Mollusca, Gastropoda) para el Perú. Puclicaciones Del Museo de Historia Natural Unmsm A, Lima, Perú, n.41, p. 5.; Ramirez et al. 2003RAMÍREZ, R., PAREDES, C. & ARENAS, J. 2003. Moluscos del Peru. Rev. Biol. Trop. 51 (3): 225-284.) and Paraguay (Hylton-Scott & Lapuente 1968HYLTON-SCOTT, M.I. & LAPUENTE, E. 1968. Valor diagnostico de la Radula para especies del genero Omalonyx Orbigny. Neotropica 14:49-56.). Parodiz (1963)PARODIZ, J.J. 1963. Observaciones anatomicas sobre Omalonyx patera Doer., com una nota biografica acerca de Adolfo Doering (1848-1926). Sterkiana. 12:1-7. listed Omalonyx specimens from Paraguay, Argentina and Bolivia that were deposited in different institutional collections. Cazzaniga (1985)CAZZANINGA, N.J. 1985. Anotaciones sobre algunos gasterópodos no marinos de la Argentina. Comun. Soc. Malacol. Urug. 6:329-331., based on a bibliographic review, concluded that the known distribution area for O. unguis is southern Brazil, northern and eastern Argentina, Uruguay, Paraguay, and Bolivia and that the presence of O. unguis in the west of Argentina is known only in Tucumám (Hylton-Scott 1971HYLTON-SCOTT, M.I. 1971. Homalonyx weyrauchi, Nueva especie de Tucuman. Neotropica. 17:12-14.) and Catamarca Provinces. The latter represents a new record made by Cazzaniga (1985)CAZZANINGA, N.J. 1985. Anotaciones sobre algunos gasterópodos no marinos de la Argentina. Comun. Soc. Malacol. Urug. 6:329-331. himself. Arruda & Thomé (2008b)ARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166. showed that the distributions of O. convexus and O. unguis overlap in the Argentinean area of the Paraná River hydrographic region and adjacent localities in Uruguay. Gutiérrez Gregoric et al. (2013)GUTIÉRREZ GREGORIC, D.E., NÚÑEZ, V., VOGLER, R.E., BELTRAMINO, A.A. & RUMI, A. 2013 Gasterópodos terrestres de la provincia de Misiones, Argentina. Rev. Biol. Trop. 61(4):1759-1768. recorded the occurrence of Omalonyx sp. in Misiones Province, Argentina using data from the La Plata Museum Mollusk Collection, literature and his own field work. For further literature data about Omalonyx occurrence in Argentina see Table 3. There are some records of Omalonyx in Chile (Odhner 1922ODHNER, N.H. 1922. Mollusca from Juan Fernandez and Easter Island. In The Natural History of Juan Fernandez and Easter Island (C. Skottsberg ed.). Zoology. Almqvist & Wiksells, Uppsala, v.3, p.219-254., Letellier et al. 2003, 2014), and some of them are recent. However, in 1981, Tillier studied specimens from Chile that were identified as O. gayana and stated that, despite its limaciform shape, the species belongs to the genus Succinea. The recent records from Chile (Letellier et al. 2003, 2014) do not include a description of the specimens nor any discussion on this taxonomic issue related to Chilean succineids. Thus, we suppose that the specimens are in fact Succinea gayana.

The distribution of the genus in the Lesser Antilles is also well documented. Succinea haliotidea Mittre 1841 was found in Martinique by Mittre (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.). However, Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. did not include this species in the genus Omalonyx, and indicates that they do not even belong to the family Succineidae once neither he nor Fischer found any Omalonyx in Martinique. Therefore, we did not include Martinique within the occurrence area of Omalonyx. Hermann & Dundee (1967)HERMANN, P.W. & DUNDEE, D.S. 1967. Notes on Omalonyx. Sterkiana. 28:1-6. studied Omalonyx from Sta. Lucia and Antigua, both in the Lesser Antilles. Other authors have also worked in this region. Patterson (1971)PATTERSON, C.M. 1971. Taxonomic studies of the land snail family Succineidae. Malacol. Rev. 4:131-202. and Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. studied specimens from Antigua, and Robinson et al. (2009)ROBINSON, D.G., HOVESTADT, A., FIELDS, A. & BREURE, A.S.H. 2009. The land Mollusca of Dominica (Lesser Antilles), with notes on some enigmatic or rare species. Zool. Meded. 83:615-650. recorded the occurrence of Omalonyx in several localities in Dominica. Arruda et al. (2016)ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019. showed new records of O. geayi and extended the range of distribution of this species in South America to include Suriname, Ecuador, and Bolivia. All references and localities are in Table 3.

2. Records from institutional collections

Based on data of Brazilian institutional collections obtained through literature, museum databases or onsite research, we verified 21 records for the genus in the North region of the country, 28 in the Northeast, four in the Central West, 33 in the Southeast and 31 in the South (Table 2). Specimens were found in eight Brazilian institutional collections (INPA, MCP, MCNZ, MZSP, MNRJ, UFS, ZUECA and CMIOC). Among the institutional collections that were visited, two of them did not present specimens belonging to the genus (MIRR and MPEG) in (Table 1). Brazilian specimens of Omalonyx were also registered in six foreign institutional collections (ANSP, FMNH, BMNH, ZMB, MNHN, and MCZ). We also investigated the presence of Omalonyx in other South American countries and Lesser Antilles using engines for virtual searching in databases from Brazilian (CMIOC, MCP, MZSP, MNRJ) and foreign institutional collections (ANSP, BMNH, USNM, CM, MACN, MLP) (Table 3).

3. Malacological surveys in Brazil

Specimens of Omalonyx were sampled across Brazilian hydrographic regions, and the sites were classified above according to the presence or absence of Omalonyx spp. (Table 2 and 5).

Table 5
Surveyed sites within the Brazilian administrative regions where Omalonyx spp. was absent.

3.1. Surveyed sites with Omalonyx spp. presence

Specimens were collected in all Brazilian geographic regions, and we found Omalonyx in three States of the South region (Rio Grande do Sul, Santa Catarina, Paraná) where six localities were sampled, one State in the Southeast region (Minas Gerais) where seven localities were sampled, two States in the Central-west region (Mato Grosso, Mato Grosso do Sul) where four localities were sampled, five States in the Northeast region (Piauí, Ceará, Rio Grande do Norte, Pernambuco and Bahia) where nine localities were sampled, and five States (Acre, Amazonas, Pará, Rondônia and Amapá) in the North region where 15 localities were sampled. Among these localities, we made new records for four Brazilian States: Acre, Rondônia, Amapá and Piauí. All coordinates for 41 surveyed sites are listed in Table 2 and indicated in the map (Figure 1).

3.2. Surveyed sites with Omalonyx spp. absence

Despite the surveying effort, there were no records of Omalonyx spp. in three States: Distrito Federal (Central-west region), Tocantins and Roraima (North region). The coordinates are shown in Table 5.

4. Modeling of species distributions

The potential distribution of each species is indicated in the maps (Figure 2) where different colors and color densities are related to different probabilities of occurrence of suitable conditions for their presence. The environmental model applied here agrees with the data on species distribution (Figure 1) and supports geographic constraints on the species. Some species presents overlapping ranges of distribution. This is the case for O. matheroni, O. pattersonae and O. geayi, which tend to occur in tropical areas within the northern half of South America (Figure 2A, B and C) and for O. convexus and O. unguis, which tend to occur in temperate areas in the southern half of South America (Figure 2 D and E). Omalonyx matheroni, O. pattersonae and O. geayi present moderate probability of occurrence in a vast area within northern South America, merged with intermittent areas of high probability of occurrence (Figure 2A, B and C). Omalonyx convexus and O. unguis present a smaller area of occurrence; however, there are many regions of high probability of occurrence.

Figure 2
Potential distribution of Omalonyx species modeled with Bioclim analyses using all 19 bioclimatic variables, altitude and the full dataset showed on tables 2 and 3. (A) Omalonyx matheroni; (B) Omalonyx pattersonae, (C) Omalonyx geayi, (D) Omalonyx convexus, (E) Omalonyx unguis. The numbers represents the mainwatersheds within South America. The hydrographic regions are indicated by numbers: 1) Pacific Coast; 2) Caribbean sea; 3) Orinoco River; 4) Amapá-Esequibo; 5) Amazon River; 6) Tocantins River; 7) North Atlantic; 8) São Francisco River; 9) Eastern Atlantic; 10) Del Plata; 11) Border strip of the Brasilica (North) and the Chilean-Patagonian (South West) Subregion; 12) Eastern; 13) Chilean-Patagonian Subregion of the Pacific Versant; 14) Chilean-Patagonian Subregion of the Atlantic Versant.

There was a high probability of occurrence of O. matheroni in the Lesser Antilles, in the central region of South America (hydrographic region 5 and 10), in the Atlantic coast (hydrographic region nine), and in the south of South America (hydrographic region 13) (Figure 2A). These areas are predominantly tropical; however, there are also some temperate areas.

Omalonyx pattersonae showed a high probability of occurrence in tropical and arid regions (Figure 2B) in hydrographic region one, two and three (at isolated points in arid regions within hydrographic regions two and three) and in hydrographic regions six, seven and eight (in tropical and arid regions). Moderate probabilities of occurrence of O. pattersonae were observed in hydrographic regions nine and five (tropical region), where discontinuous areas of high probability of occurrence were observed in the Amazonian region (tropical and arid region) (Figure 2B).

Omalonyx geayi is a predominantly tropical species that can also occur in arid areas with high probability of occurrence within hydrographic regions one, two, three, four and five (Figure 2C). In hydrographic region five there are several small areas of high probability of occurrence merged in a vast area of moderate probability. There are areas of moderate probability of occurrence of O. geayi in hydrographic regions six, seven and 13.

Temperate areas along the southeast of South America present the highest probability of O. convexus occurrence. Areas with high probability of occurrence are within hydrographic regions 10, 12 and 13 (Figure 2D). There is moderate probability of occurrence in a vast area of hydrographic region 10 and in small areas within hydrographic regions 11 and 13.

Temperate areas in the southeast of South America that presented high probability of O. unguis occurrence includes hydrographic regions 10, 11, 12 and 13 (Figure 2E). Some areas within tropical (hydrographic regions five, nine and 10), arid (hydrographic region 11) and temperate areas (hydrographic region 14 and Malvinas Islands) were considered to have moderate probability of occurrence.

The PCA analysis resulted in three layers with highest eigenvalues that better explain the relationship between the variables in the selected study area. The most representative variables within these PCA-analysis axes were BIO4 (Temperature seasonality), BIO12 (Annual precipitation), and Altitude. As a consequence, the modeling of the species of Omalonyx was strongly influenced by these three variables, and their potential distribution was mainly determined by them. There is only one record of O. brasiliensis, thus, it was not possible to model this species' distribution due to technical limitations.

Discussion

This work addresses Omalonyx species distribution. The genus has a widespread Neotropical distribution, covering most South American hydrographic regions (except hydrographic regions one and 14) and the Lesser Antilles. The species occurrence map and the model of species distribution showed that three species are related to the north of South America (O. matheroni, O. pattersonae, O. geayi) and Lesser Antilles, and three species are related to the south of South America (O. unguis, O. convexus, O. brasiliensis).

Omalonyx matheroni is the most widespread species, and its distribution is more concentrated in northern South America (North and Northeast of Brazil, Guyana, French Guiana and Suriname) and in the Lesser Antilles. Omalonyx matheroni occurs in all Brazilian hydrographic regions. The most southern record for this species is Santa Catarina State in the south of Brazil (12, Figure 1).

Among northern species, O. matheroni is the most widespread. On the other hand, the records for O. geayi and O. pattersonae are discontinuous. Despite a huge area with high or intermediate probability of occurrence (Figure 2), the records for O. pattersonae and O. geayi are sparser (Figure 1). Omalonyx geayi was known to occur only in Kaw Swamp, French Guiana, the type locality (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.). However, new records published recently expanded its distribution to Ecuador, Bolivia, Suriname and some localities in Brazil (Arruda et al. 2016ARRUDA, J.O., BARKER, G.M. & THOMÉ, J.W. 2016. Revaluation of the taxonomic characters and distribution of Omalonyx geayi Gastropoda, Succineidae). Iheringia, Sér. Zool. 106:2016019.). In this work, we recorded O. pattersonae for the first time in three hydrographic regions in North and Northeast of Brazil. There is one state in Brazil (Amazon State) where all three of these species occur at sites that are very close.

The other three species (O. unguis, O. convexus, O. brasiliensis) are concentrated in the south of South America. Among these species O. unguis reaches the most northern positions. This species was even found outside its distribution range (Lesser Antilles, Bolivia, Peru and in Ceará State, in the Northeast of Brazil). Omalonyx convexus records are very concentrated (Figure 1) and are restricted to sites where high or intermediate probability of occurrence was predicted (Figure 2B). However, there are some exceptions, and the species was also recorded in the north shore of Venezuela and in the Northeast of Brazil (Sergipe State). Until now, O. brasiliensis was known only from its type locality in Rio Grande do Sul State, Brazil. Despite all the surveying efforts already concentrated in Rio Grande do Sul State (Figure 1), O. brasiliensis was never found again since its description and the species remain known only for the type specimens from an unspecified site that could be related to hydrographic region 10 or 12 (Figure 1). Thus, O. brasiliensis remains to be rediscovered. This is a large State where O. convexus is widespread (Table 2, Figure 1); thus, both species may occur in sympatry.

There are several records from literature review, museums and collections that were not identified to species level and are designated Omalonyx sp. They were not used to model species distribution. These records are widespread throughout South American hydrographic regions (e.g., five, seven, nine and 10) and should also be carefully analyzed in future studies. On the other hand, some records identified to species level seem to be inconsistent (e.g., O. convexus was recorded for the Northeast of Brazil) and should be revised. All the records situated outside the area predicted for the species distribution should be carefully investigated. We suppose that the lack of taxonomists dealing with this group is the main cause for the great amount of records identified to genus level. On the other hand, the lack of training and the subtle morphological differences among species must be a cause of misidentification. These problems contribute to gaps in the knowledge regarding Omalonyx distribution (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146., Coscarelli & Vidigal 2011COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.).

Brazil is the best-sampled region in South America. Here, based on our malacological surveys, new records were made in Acre, Rondônia, Piaui, and Amapa. However, despite the absence of records even after intensive surveys in some administrative unities (Roraima, Tocantins and Distrito Federal) (Table 5), the genus was registered in all Brazilian hydrographic regions. There were no records for the central area of Tocantins River hydrographic region (surveyed sites: Palmas and other surrounding areas such as Lagoa da Confusão and Porto Nacional). However, the genus was present in the upper part of the hydrographic region (comprising Goiás and Pará States; Figure 1 and Table 2). Distrito Federal is an administrative unity that encompasses a small area when compared to the Brazilian States, and within this small area, there are the frontiers of three hydrographic regions: Tocantins River, São Francisco River and Del Plata. Despite its proximity to Goiás State where we found Omalonyx sp., there were no records in Distrito Federal (surveyed sites: the margins of Paranoá Lake, in Brasília, and in Brazlândia, all of them in the upper Del Plata hydrographic region where the genus is widely distributed; Figure 1). In Roraima State, northern Brazil, despite the surveying efforts (23 records of absence) no record was made. Roraima is within the Amazon River hydrographic region in which Omalonyx is widely distributed (Figure 2). However, all these negative localities are in the northeastern quadrant of Roraima, which is characterized by unusual vegetation, a seasonally flooded savannah, locally called “Lavrado” (Barbosa et al. 2007BARBOSA, R.I., CAMPOS, C., PINTO, F. & FEARNSIDE, P.M. 2007. The “Lavrados” of Roraima: Biodiversity and conservation of Brazil’s Amazonian Savannas. Func. Ecosyst. Commun. 1:29-41.), which may have some ecological features that prevent Omalonyx spp. colonization. Future sampling efforts should focus on areas within these States that were not investigated until now. Considering that Omalonyx spp. occur in the hydrographic regions that cover these States, the absence of records is probably due to insufficient sampling effort.

In South America Omalonyx species were found in all hydrographic regions (except hydrographic regions one and 14) and countries. However, there were only isolated records in Colombia, Ecuador and Chile, indicating the need for more sampling effort in these areas (Figure 1). However, the occurrence of this genus in Chile must be further investigated due to different point of views regarding the identification of the Chilean slug-like succineids (Tillier 1981TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.). The record from Chile (Letellier et al. 2014) should be carefully investigated since Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146. considered that the species recorded in Chile, O. gayana, belongs to the genus Succinea. In fact, Chile is separated from the other South American countries by the Andes mountain range, which is the major water divider in South America. d’Orbigny (1837)D`ORBIGNY, A. 1837. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3. P. Bertrand, Paris, France. stated that the genus occurs only on the east side of the ridge, and until now, there is no evidence suggesting otherwise. Our results agree with those from d’Orbigny (1837)D`ORBIGNY, A. 1837. Voyage dans L’Amerique Méridionale: Mollusques. v.5, Partie 3. P. Bertrand, Paris, France. and Tillier (1981)TILLIER, S. 1981. South American and Juan Fernandez succineid slugs (Pulmonata). J. Molluscan Stud. 47:125-146.. Bioclimatic analysis proved to be a valuable tool for gaining insight into the geographical distribution of a species, especially when few records are available (i.e., O. geayi and O. pattersonae). Predictions showed that O. matheroni and O. geayi are tropical species. Omalonyx pattersonae usually occurs in arid regions; however, its distribution moderately extends over tropical areas. However, the prediction of O. geayi to hydrographic region 13 (temperate and very cold area) could be related to low numbers of records. In fact, bias can occur if species are insufficiently sampled. Thus, climatic envelopes may generate incomplete results, and the accuracy of predicted distributions will be decreased (Beaumont et al. 2005BEAUMONT, L.J., HUGHES, L. & POULSEN, M. 2005. Predicting species distributions: use of climatic parameters in BIOCLIM and its impact on predictions of species’ current and future distributions. Ecol. Model. 186:250-269.).

The occurrence records and the predictions both indicated that O. convexus and O. unguis have largely overlapping distributions in temperate areas within southern South America. These results are in accordance with those from Arruda & Thomé (2008b)ARRUDA, J.O. & THOMÉ, J.W. 2008b. Revalidation of Omalonyx convexus (Hynemann 1868) and emendation of the type locality of Omalonyx unguis (Orbigny 1837). Arch. Moll. 137:159-166. and Coscarelli & Vidigal (2011)COSCARELLI, D. & VIDIGAL, T.H.D.A. 2011. Mollusca, Gastropoda, Succineidae, Omalonyx unguis (d’Orbigny, 1835): Distribution extension and new records for Brazil. Check List. 7:400-403.. However, the distribution of O. convexus is constrained to temperate regions while O. unguis is well represented in tropical, temperate and arid regions indicating that the latter presents a broader tolerance range for environmental variables and is adapted to different bioclimatic conditions.

Considering the extension and the great diversity of habitats in the neotropical region and the wide occurrence area of Omalonyx species, bioclimatic models can be used to extrapolate information on species distribution if the high cost of field surveys in such a vast area is unfeasible. Information on the distribution of Omalonyx species will help to improve the taxonomic and biogeographic studies on these slug-like gastropods.

Acknowledgements

We are grateful to all colleagues that collected and sent material from different localities: Silvana Thiengo, Mônica Fernandez, Jean P. Pointier, Andrea Roche, Diego E. Gutierrez, Fernando S. Bezerra, José Cassimiro, Henry P. Lima, Felipe S. F. Leite and Villand Bergerhoff. We are also grateful to the curators of the institutional collections Célio Magalhães (INPA), Luiz R. Simone (MZSP), Arnaldo Coelho and Norma Salgado (MNRJ), Alejandra Rumi (MLP). Special thanks to Sílvia Gandolfi and Sônia Buck for the valuable support, to Daniel M. Pimpão, Fernando I. Martins, Linus Spatz and Mônica Tassara for important assistance in field collections, Adalberto dos Santos and Jennifer T. M. Andrade for text review. This work was partially supported by grants from FAPEMIG.

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Publication Dates

  • Publication in this collection
    2018

History

  • Received
    24 July 2017
  • Reviewed
    16 Oct 2017
  • Accepted
    23 Dec 2017
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