Land Snail Fauna Research Articles

Protoconch sculpture as a taxonomic tool in Australian charopid systematics (Gastropoda: Eupulmonata: Charopidae)

ABSTRACTCharopidae represent one of the most speciose land snail faunas in Australia with an estimated 750 species, mostly being less than 5 mm in shell diameter. The majority of its species are undescribed. With limited available material suitable for molecular analysis, morphological methods remain the primary technique for the identification of charopid species, and recent studies have shown that the sculptural patterns on the protoconch are diagnostic in establishing a generic signature. This study attempts to establish a formal framework for the description of the protoconch patterns for those species currently considered to be members of the eastern Australian Gyrocochlea sensu lato (s.l.) group of charopids. The protoconch sculpture of 60 species and 72 putative species of Gyrocochlea s.l. were examined and grouped by sculptural pattern and location. Eleven major configurations are identified, defined and described. It is intended that this terminology will be the benchmark for future descriptions of the protoconch characteristics of Australian charopid species and their generic placement. Implications for the past generic allocation of some Gyrocochlea s.l. species are discussed. Evidence from this study also indicates that there is local geographic consistency in the distribution of the protoconch patterns and a broad latitudinal sequence of pattern turnover. The biogeographic implications of this are briefly explored.

Bellwether of the Canaries: anthropogenic effects on the land snail fauna of the Canary Islands

Natural areas near human-modified landscapes experience factors that may affect local biodiversity at levels commensurate with natural environmental factors. The land snails of the Canary Islands provide excellent opportunities to evaluate the importance of anthropogenic agents in mediating the diversity and distribution of species. Land snails are particularly sensitive to disturbance and are an integral part of terrestrial ecosystems. This study analyzed the distributions and abundances of terrestrial macrosnail shell assemblages at 60 localities throughout the coastal scrub biome of the Canary Islands. This was accomplished using data on natural and anthropogenic variables to assess their relative importance in governing land snail diversity. A total of 34,801 dead shells represented a diverse malacofauna with highly localized endemism. Due to uncertain species identifications, samples from the 18 sites from the two easternmost islands are described, but excluded from statistical analyses. Regression tree analysis indicated that proximity to agricultural sites was the most important predictor of species diversity. Sites with no or very little agricultural area (≤ 0.167 km2) within a 1 km radius had significantly higher richness and diversity. These results have implications for Canary Islands conservation. Protected areas that are patchworks of natural and agricultural landscapes are still subject to native biodiversity loss because of anthropogenic impacts even when the footprint of agriculture is small.

Calcareous forest seepages acting as biodiversity hotspots and refugia for woodland snail faunas

Land-snail species richness has repeatedly been found to increase with the increasing site calcium content and humidity. These two factors, reported as the main drivers of land-snail assemblage diversity, are also among the main habitat characteristics of calcareous seepages. Here we explore local species richness and compositional variation of forest spring-fed patches (i.e. seepages), to test the hypothesis that these habitats might act as biodiversity hotspots and refugia of regional snail faunas. In contrast to treeless spring fens, only little is known about land snail faunas inhabiting forest seepages. Studying 25 isolated calcareous forest seepages, evenly distributed across the White Carpathians Protected Landscape Area (SE Czech Republic), we found that these sites, albeit spatially very limited, can harbour up to 66% of the shelled land-snail species known to occur in this well-explored protected area (in total 83 species). By comparing land snail assemblages of the studied seepages with those occurring in the woodland surroundings of each site as well as those previously sampled in 28 preserved forest sites within the study area, we found the seepages to be among the most species rich sites. Although the numbers of species did not statistically differ among these three systems, we found highly significant differences in species composition. Seepage faunas were composed of many species significantly associated with spring sites, in contrast to the assemblages of both surrounding and preserved forest sites. Our results highly support the hypothesis that calcareous forest seepages might serve as refugia and biodiversity hotspots of regional land snail faunas. Protection of these unique habitats challenges both conservation plans and forest management guidelines as they might act as sources for the recolonization and restoration of forest snail assemblages particularly in areas impoverished by harvesting and clearcutting.

Type Specimens of Hawaiian Land Snails in the Smithsonian Institution, National Museum of Natural History, with Lectotype Designations

Pacific island land snail faunas are among the most threatened faunas in the world, having suffered a higher rate of extinction than any other major animal group. The Hawaiian land snails are among the most species-rich and most severely effected of these faunas, yet the current status of most of the Hawaiian species is unknown. Most of the major taxonomic studies on the fauna were undertaken 50–100 years ago and only certain groups were comprehensively studied. New research is uncovering undescribed species, both extant and extinct. The need for rigorous taxonomic treatment of the group is acute if the taxonomic and conservation status of the many species is to be ascertained, and the basis for such research is comprehensive study of type material. The Smithsonian's National Museum of Natural History holds type material of 39 nominal species-group taxa of Hawaiian land snails belonging to eight families; this annotated catalog provides details of this material. Of these taxa, 29 were described by Augustus Addison Gould from material collected by the U.S. Exploring Expedition of 1838–1842. For completeness, we also provide details for one lot of purported paralectotypes that are here inferred not to have been syntypes and one lot representing an unavailable infrasubspecific name. We designate lectotypes for 12 species-group taxa . Yeung, Norine W., Robert H. Cowie, Kenneth A. Hayes, and Ellen E. Strong. Type Specimens of Hawaiian Land Snails in the Smithsonian Institution, National Museum of Natural History, with Lectotype Designations. Smithsonian Contributions to Zoology, number 647 , vi + 34 pages, 11 figures, 2017.

Diversity and taxonomy of Vietnamese Pollicaria (Gastropoda, Pupinidae)

Species in the genus Pollicaria (Gastropoda: Pupinidae) are conspicuous members of the southeast Asian land snail fauna. Originally erected in 1856, both the genus and its constituent species have been reorganized multiple times with the most recent treatment published in 2013. Collections of Vietnamese Pollicaria during 2014 and 2015 raised questions of the utility of currently used diagnostic shell characters and identification keys in species identification. An examination of the authors’ collections, combined with museum specimens, suggested that at least three species of Pollicaria occur or have historically occurred in Vietnam. It is suggested that P. rochebruni is a senior synonym of P. crossei and treat both taxa as conspecific. A second species, P. mouhoti, was believed to only occur in Cambodia, Laos, and Thailand. A possible third species, based only on previous karyotypic work, is discussed. Our data further suggest that shell features such as color and size lack consistent utility in species-level identifications in Pollicaria.

The composition and richness of the land-snail fauna of gallery forest along the Muvumba River in Rwanda

The composition and richness of the land-snail fauna of gallery forest along the Muvumba River in Rwanda

Paleobiogeography of Early/Middle Miocene terrestrial gastropods in Central Europe: An approach using similarity indices

Terrestrial gastropods are a common faunal element in continental Miocene fossil Lagerstätten of Europe. Although having lived during a time span that includes the Miocene Climatic Optimum and the devastating Ries/Steinheim meteorite impacts, the state of knowledge about their faunal composition and geographic distribution is surprisingly incomplete. The land snail faunas of 30 different Early and Middle Miocene deposits of Central Europe (European Mammal Neogene zones MN 4 to MN 8) were compared using statistical methods (cluster and NMDS analyses, using the Ochiai, Simpson and Kulczynski indices). This includes 300 different taxa identified so far. Most of the analyzed deposits were part of the Miocene Paratethys and are today located in France, SW Germany (Baden-Württemberg state), SE Germany (Bavaria state), Austria, Poland, and Hungary. Cluster analyses resulted in different clusters, the majority of which can be explained by their geographic situation and/or by their distribution in time (e.g., the consistently recovered Baden-Württemberg and Bavaria clusters and the Bakony Mountains cluster). The remaining clusters cannot be fully explained so far, but some possibilities are explored here. Our results reveal the power of a solid taxonomic framework as a basis for palaeobiogeographic studies. As such, more “basic” palaeontological studies are required to strengthen future analyses.

Drivers of Central European urban land snail faunas: the role of climate and local species pool in the representation of native and non-native species

The importance of macroclimate and dispersal limitation in the broad-scale variation of European urban land snail assemblages is likely to differ between native and non-native species because of the southern origin of many non-native snails, often spread by humans. We sampled land snails in each of 32 European cities and compiled from the literature a list of land snail species reported from the surroundings of each city. To quantify the predictive power of climate and local species pools, beta-sim dissimilarity matrices of both native and non-native species were explored using MDS and RDA ordination methods, Mantel tests with bootstrapping of each dataset, and multivariate homogeneity analysis of group variances. We observed no significant relation between the numbers of non-native species found in the cities and their surroundings (p > 0.133), while the percentage of native species in the cities derived from their local species pools decreased significantly with the increasing species richness of local faunas (rS = −0.75, p < 0.001). Assemblage variation of urban native species was explained mostly by the difference between mean January and July temperatures (21.3 %), with the major role of July temperature (18.0 %). In contrast, variation of non-native species assemblages was mainly explained by January temperature (19.9 %). The congruence in faunal similarities between the cities and the surrounding areas was higher in native (r = 0.46, p < 0.001) than in non-native species (r = 0.36, p < 0.001). Overall native faunas were significantly more homogeneous than the non-native faunas. Our results suggest that recent climate warming may foster geographical expansions of many non-native land snail species as their distributions are controlled mainly by January temperature.

Annotated catalogue of types of Hawaiian land and freshwater snails (Mollusca: Gastropoda) in the Muséum national d'Histoire naturelle, Paris, with lectotype designations

ABSTRACT Pacific island land snail faunas are among the most threatened faunas in the world, having suffered a higher rate of extinction than any other major animal group. The Hawaiian land snails are among the most species rich and most severely impacted of these faunas, yet the current status of most of the Hawaiian species is unknown. Most of the major taxonomic studies on the fauna were under-taken 50–100 years ago and only certain groups were comprehensively revised. New research is uncovering undescribed species, both extant and extinct. The need for rigorous taxonomic treatment of the group is acute if the validity and conservation status of the many species is to be ascertained, and the basis for such research is comprehensive study of type material. The Museum national d'Histoire naturelle, Paris, holds type material of 38 nominal species-group taxa of Hawaiian land and freshwater snails belonging to six families, overwhelmingly the Achatinellidae Gulick, 1873 and Amastridae Pilsbry, 1910; this a...

Discordance between morphological and taxonomic diversity: land snails of oceanic archipelagos

AbstractAimMorphological and taxonomic diversity are intuitive measures of biological diversity. Previous studies have shown discordance between these measures at large spatial and temporal scales, but the implications of this pattern for the underlying processes are not understood. Using oceanic archipelagos as spatial units, we examine potential links between the morphological and taxonomic diversity of their land snail faunas in a biogeographical framework.LocationEleven major oceanic archipelagos.MethodsFor each archipelago, we assembled lists of indigenous land snail species, classified by family and genus, with shell height and width for each species (1723 species in total). We used biogeographic and climatic variables as potential predictors of diversity patterns. We employed regression analyses to evaluate (1) whether morphological diversity scales with taxonomic diversity at the species, genus or family level, and (2) whether morphological and taxonomic diversity correlate similarly with biogeographic/climatic factors. We also assessed which taxonomic level contributes most to morphological variation within archipelagos.ResultsMorphological diversity across archipelagos was strongly related to genus but not species richness. Within archipelagos, morphological variation reflected differences among genera and families but not species. Species richness was best explained by archipelago area, but morphological diversity was not significantly related to any of the physical features of archipelagos.Main conclusionsAcross archipelagos, species richness and morphological diversity of land snail faunas are decoupled. The relationship between species richness and the available ecological space (captured mainly by area) indicates the prevalence of niche‐based processes while, for morphological diversity, the strong conservatism of morphology at the genus level suggests the presence of diversification‐based limits. Assuming genera effectively reflect diversification, our findings indicate that morphological space on oceanic archipelagos depends primarily on the number of evolutionary units that have colonized and/or diversified through time.

Disappearing jewels: an urgent need for conservation of Fiji’s partulid tree snail fauna

Where conservation status of island non-marine molluscs is known, snails tend to be one of the most threatened faunal groups. However, published information regarding island gastropod conservation status, diversity and endemism is frequently unavailable despite the importance of this information for the formulation of biodiversity action plans and conservation strategy. Fiji, for example, has a diverse native land snail fauna (&gt;240 species) with an endemism level of ~80%, but only within the last few years has any information about any of these species been available to the national biodiversity reporting repository. For one lineage in particular, members of the tree snail family Partulidae, with four endemic Fiji Island species, the conservation status of the group has never been assessed. However, based on the alarming extinction rates documented in partulid snail species on other Pacific Islands, information about the occurrence and status of these taxa is urgently needed for Fiji’s biodiversity action plan. To redress this information void, we formulated the Fijian Partulid Tree Snail Project, consisting of five components: (1) raising awareness; (2) locating populations and monitoring population trends; (3) elucidating patterns of genetic diversity; (4) creating action partnerships; and (5) conducting disturbance gradient analyses. The overall goal was to characterise mechanisms leading to persistence of partulids in the face of increasing anthropogenic disturbance. In the initial stages of this project, existing information on Fiji’s partulids was collated and two small, remote islands in the Fiji archipelago were surveyed to investigate whether tree snails persisted there. Living populations of Partula lanceolata and empty shells of Partula leefei were found on Cicia Island in Lau, and on Rotuma Island in the Rotuma Group, respectively. DNA analyses confirm a sister relationship between the two Partula species in north-eastern Lau, P. lirata and P. lanceolata, with both sharing a sister relationship with a member of the same genus in Vanuatu – P. auraniana Hartman, 1888. Prioritisation and further sampling of additional islands, and residual native habitat on less accessible islands and islets, is needed to fully assess the conservation status of all four Fijian species via the IUCN Red List process. Moreover, the basic descriptive information and associated studies reported here will serve to raise awareness of Fiji’s endemic tree snails particularly in communities that had no prior knowledge of their special conservation status; and also at a wider national, regional and global level. Community awareness is particularly vital as the willing support of land owners in the relevant small island communities is critical to implementing any future conservation action plans.

Diversity patterns in the land-snail fauna of Afromontane forest in the Rwenzori Mountains in Uganda

We investigated the land-snail fauna in Afromontane forest along three transects on the eastern slopes of the Rwenzori Mountains in Uganda. Forty plots at altitudes between 1,770 and 2,932 m were studied. A total of 4,823 specimens were collected and were assigned to 91 land-snail species. Considering additional literature records, the land-snail fauna of the Rwenzori Mountains includes at least 174 species (142 on the Ugandan side). Currently, no area in Africa of a similar size is known to harbour such high regional land-snail species richness. The high species richness and endemism are partly the result of radiations of several Afromontane groups within the Rwenzori Mountains. The regional richness in the Albertine Rift is mainly affected by the distance from Pleistocene forest refugia. The majority of the species recorded in the Rwenzori Mountains extends from the lowest investigated altitudinal levels to different upper altitudinal levels, but there are also groups of species that are restricted to higher altitudes. Thus, the change of the composition of the land-snail communities along the altitudinal gradient is not completely gradual, but there is a rapid turnover in parallel with the transition from the montane rainforest zone to the bamboo zone. Whereas minute Afromontane species often have wide, disjunct distributions across East Africa, larger sized Afromontane snail groups are usually represented by endemic species in different mountain ranges. The better passive dispersal abilities of microsnails probably resulted in a higher gene flow between mountain ranges, resulting in coherence of the populations and a reduced likelihood of speciation.

History of two critically endangered grassland snails (Pulmonata: Helicellinae) in the Czech Republic with first molecular data on extinct populations

AbstractThe composition of the land snail fauna of central Europe is responsive to environmental conditions and undergoes changes throughout the Holocene. That holds also for the fauna of central-European Helicellinae, a group of dry-adapted western Palearctic snails with five species living in the Czech Republic. While one of them is currently spreading in the country, two, Candidula unifasciata and Helicopsis striata, are critically endangered, both with only a single surviving population. Although sharing a similar fate lately, these two species represent completely different histories. While C. unifasciata is a rather recent immigrant in the area, H. striata is a relict species of the Pleistocene loess steppe, which is declining during the Holocene. However, the origin of the only known extant Czech population of H. striata is deemed to be dubious due to the untypical habitat inhabited, and within C. unifasciata two species or subspecies used to be distinguished, suggesting a dual origin of its populations. We present here sequences of a fragment of the 16S rRNA gene from two extinct and the last surviving populations of H. striata, and from two extinct populations of C. unifasciata from Bohemia, supplemented by Slovak samples of both. The obtained haplotypes of Bohemian C. unifasciata are different from the one found in western Slovakia, suggesting a different origin of the Western Carpathian populations. The sampled extinct Bohemian populations of H. striata shared an identical haplotype with the last living population, supporting native origin and conservation value of the latter. The causes of the disappearance of the two species are discussed

Impact of climate change on the distribution of a giant land snail from South America: predicting future trends for setting conservation priorities on native malacofauna

Many land snails are vulnerable to climate change as a consequence of small distribution ranges and poor dispersal. South America is a diverse region in terms of land snail fauna, but studies about the impacts of climate change on molluscan biodiversity are virtually nonexistent. Bioclimatic models provide an important tool to assess how habitat suitability may change in a warming planet. In this study, we examine potential impacts of climate change on a giant land snail (Megalobulimus sanctipauli) from the Atlantic Forest to predict future shifts in its potential distribution, and to identify protected areas that may contain suitable habitat for setting conservation priorities. Using a maximum entropy algorithm, we modeled the species' potential distribution across South America under current climatic conditions and projected the results onto two climate change scenarios for two time frames. A 2.17 % of South America on the Atlantic Forest was predicted to be currently suitable for the species, comprising the border area among Argentina, Brazil and Paraguay. Prognosis of future distribution showed a trend to a northern retraction, but a southern expansion of current potential range. More than 150 protected areas were identified to contain climatically suitable habitat for the species, but on the less optimistic outlook only ~1545 km 2 of protected areas (0.009 % of South America) would remain suitable for the species by the end of the century. Our findings are expected to improve understanding of climate change impacts on native giant land snails and to contribute in conservation efforts on this malacofauna.

At the Central European-Balkan transition: forest land snail faunas of the Banat contrasted with those of the Carpathian chain

Twenty-nine forest sites in six sampling areas in the Banat region of Romania, adjacent to Serbia, were sampled to obtain inventories of their snail faunas and to make comparisons between these and previously studied faunas in the mountains from the Sudetes in the north-west to the Southern Transylvanian Carpathians in the south. 65 species were recorded overall, with between 13 and 33 at individual sites. Among the six sampling areas that on Schist rock at high altitude differed markedly from the others, and contained mainly species also found in Carpathian forests further north. The remainder, mainly on limestone, also differed among themselves, but contained more species endemic to the region or regions to the south, together with those found mainly in open rocky habitats further north. Some species and subspecies were restricted to particular areas within the region, and although ecological factors accounted for some of these differences, they did not explain all of them. The faunas were differentiated from those in the Carpathians further north, and showed a greater affinity to those from countries to the south. These patterns indicate a transition between northern regions with locally rich but regionally poor forest faunas and those of the Balkans and Mediterranean with many restricted endemics that survived the climatic fluctuations of the Pleistocene in situ. Such faunas are no richer at site level than those from further north, but differ more among themselves even when environmental conditions are similar.

Terrestrial gastropods of Srebarna Nature Reserve, North-Eastern Bulgaria (Gastropoda).

We give the results from the first investigation focused on the land snail fauna in Srebarna Nature Reserve in Bulgaria. A total of 23 localities were studied and 27 species of terrestrial gastropods were found, 23 of which were new observations for the Reserve.

Diversity patterns of the terrestrial snail fauna of Nyungwe Forest National Park (Rwanda), a Pleistocene refugium in the heart of Africa

We investigated the land snail fauna of Nyungwe Forest National Park in south-western Rwanda. Fifty plots at altitudes between 1718 and 2573 m were studied. In total, 3461 specimens were collected and were assigned to 102 land snail species. With respect to land snail species, Nyungwe Forest is the richest forest known in Africa. A comparison with other forests in the northern Albertine Rift indicates that land snail species richness in this region is significantly correlated with distance from Pleistocene forest refugia. The high beta diversity in Nyungwe is the result of a high species turnover between sites, which has biogeographical and ecological origins. Nyungwe Forest is situated on the Congo–Nile divide where species of different geographical origin may meet. Moreover, Nyungwe Forest offers a high diversity of habitats because it extends across a wide range of altitudinal zones. Species richness decreased with increasing altitude. It was also correlated with the presence of bare rocks that offer additional microhabitats and shelter. Although the occurrences of different land snail species in Nyungwe Forest were significantly clustered, only a minority of the species could be assigned to a group of species with similar occurrences. The majority of the species respond individualistically to environmental variables. The significant nestedness of the occurrences of the land snail species in Nyungwe was mainly correlated with altitude. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 363–375.

Survey of the land snail fauna (Gastropoda: Pulmonata) of Mount Kaputar National Park in northern inland New South Wales, Australia, including a description of the listing of Australia's first legally recognised endangered land snail community

Mount Kaputar is an isolated high-elevation mesic refuge on the dry inland western slopes of eastern Australia's Great Dividing Range. A field survey in Mount Kaputar National Park in 2007–2014, and collation of existing information, identified a native land snail fauna of 24 species (seven families), including nine endemic taxa and another two occurring as disjunct populations. Additional species probably remain to be identified. Two introduced species of agriolimacid slugs were also recorded. Information from this study was the basis of the successful listing of an endangered land snail community at Mount Kaputar under state threatened species legislation in 2013; the first legal listing of an endangered land snail community in Australia. The recognition of endangered communities is a useful intermediate scale between the extremes of the single-species and broad-landscape conservation approaches, and has significant potential for multi-species conservation initiatives for terrestrial gastropods. Anthropogenic climate change is the most significant threat to this community, with a 100 m rise in environmental envelope likely to reduce the available area of habitat by over 50%. This community, and, in particular, a bright pink endemic athoracophorid slug, is contributing to raising public awareness of the threat to global biodiversity from anthropogenic climate change.

Quaternary perspectives on the diversity of land snail assemblages from northwestern Europe

The land snail assemblages in NW Europe exhibit marked gradients in diversity related to both latitude and longitude. These gradients, in turn, are linked to regional differences in temperature and moisture, although other non-climatic factors may be involved. Such diversity patterns have been described for the modern land snail faunas of NW Europe, especially those that inhabit forest. Here we provide an historical perspective on the development and composition of comparable land snail assemblages from various interglacials from the Middle and Late Pleistocene, and from the Holocene. We review the land snail assemblages from tufa sequences, which provide the best faunal records for each of the temperate periods. Data from 32 Quaternary sites in 7 NW European countries are considered. Assemblages from ‘forest optima’ of Pleistocene interglacial periods are richer in species compared with those from the Holocene. Correspondence analysis (CA) of data from 25 Quaternary sites in the regions where both Pleistocene and Holocene sites occur (i.e. southern England, northern France and Germany) resulted in a geographical separation of the assemblages into a western and eastern group. CA on each geographical group resulted in chronological divisions separating Pleistocene sites from the Holocene sequences. This separation results from the occurrence of numerous Central and Eastern European species in the Pleistocene faunas, whereas Holocene assemblages are characterized by species with mostly Western and Northern European modern ranges. This difference appears to reflect climatic influences, rather than resulting from anthropogenic effects. CA of 19 Holocene tufas produced geographical clusters clearly related to their position on a west-east gradient, presumably linked to some effect of ‘continentality’. During the mid Holocene, the diversity of forest snails from tufas in southern England exceeded the totals from the richest calcareous woodland sites in the region today. Further work is needed to establish whether this pattern holds for other regions of NW Europe.

Species richness and meta-community structure of land snails along an altitudinal gradient on Bioko Island, Equatorial Guinea

We investigated the land-snail fauna of rain forests on the eastern slopes of Pico Biao on Bioko Island in the Gulf of Guinea. Thirty-seven plots were studied along an altitudinal transect reaching from sea level (lowland rain forest) to an altitude of 1,830 m (mossy forest). A total of 1,755 specimens were collected and were assigned to 68 land-snail species. Eleven species were new records for Bioko. At least 15 of the recorded species are endemic to Bioko. The degree of endemism was high in mossy forest (23%) and in lowland rain forest (20%), but lower in montane forest (8%). Species richness showed a hump-shaped distribution along the altitudinal gradient with a maximum at 500 m a.s.l. Species richness peaked in forests in which there had been selective logging more than 50 years ago, indicating that some disturbance may have beneficial effects on biodiversity. Species richness was correlated with the thickness of leaf litter. The availability and quality of suitable microhabitats is more important for the occurrence of snail species than gradients of otherwise often decisive environmental parameters like temperature, which are strongly correlated with altitude. A lack of clustering of the occurrences of different snail species along the altitudinal gradient indicated a Gleasonian meta-community structure with individualistic responses of the various species to environmental parameters. No negative co-occurrence patterns that might provide evidence for interspecific competition could be detected. The frequent coexistence of morphologically similar, and presumably ecologically equivalent, congeneric species may indicate that such equivalents do not exclude each other as predicted by the neutral theory of biodiversity. However, current knowledge about individual snail species is too scanty to exclude the possibility that niches of congeneric species differ in some details.