Gastropod Communities Research Articles

GASTROPODS COMMUNITIES IN THE MANGROVE ECOSYSTEM WAISISIL BEACH SAPARUA DISTRICT MALUKU

The gastropods community in the mangrove ecosystem on the Waisisil beach, Saparua District, Maluku consists of 14 gastropod species, namely Clypeomorus batillariaeformis, Cypraea annulus, C. moneta, Hebra corticata, Littorina scabra, Morula margariticola, Nasarius olivaceus, Natica euzona, Nerita chamaeleon, N, signata, Otoplueura auriscati, Pyrene ocellata, Strombus labiatus, Terebralia sulcata. The species with the highest number of individuals was C. batillariaeformis and the species with the lowest number of individuals was C. annulus. The gastropod community in the mangrove ecosystem on the Waisisil beach has a species diversity index (H') = 1.8, evenness index (E) = 0.7, and dominance index (D) = 0.3.

Repair scars preserve decadal‐scale patterns of predation intensity despite short‐term ecological disturbances

Abstract Recent ecological disturbances have dramatically altered the composition of rocky intertidal Pacific coast communities of North America, particularly top invertebrate predators. Predation is an important regulatory force on intertidal gastropod communities, and the depletion or loss of predators is therefore likely to have a considerable community‐wide short‐term impact. However, assessing the magnitude and nature of the resulting ecological changes may be problematic in the absence of data recording pre‐disturbance conditions. Here, the effectiveness of traces of unsuccessful crab predation on gastropod shells at providing a long‐term, decadal record of predation intensity in Barkley Sound (Vancouver Island, British Columbia) was evaluated subsequent to multiple large‐scale ecological disturbances, including sea star wasting disease, abnormally high sea surface temperatures, and harmful algal blooms. The frequency of failed crab attacks recorded by repair scars on six populations of the intertidal gastropod Tegula funebralis were surveyed to compare spatial patterns in predation intensity before and after disturbance (2013 and 2015 respectively). The repair frequency gradient observed in 2013 was also recorded by repair scars in 2015 (Spearman's ρ = 1, P = 0.002), and repair frequency was not affected by gastropod size in either 2013 (Spearman's ρ = 0.14, P = 0.80) or 2015 (Spearman's ρ = 0.66, P = 0.18). These findings are consistent with the hypothesis that repair frequency provides decadal records of predation intensity and may be effective to establish persistent levels of predation intensity prior to disturbances in rocky intertidal habitats.

The intertidal gastropods (Gastropoda: Mollusca) diversity and taxa distribution in Alas Purwo National Park, East Java, Indonesia

Abstract. Susintowati, Puniawati N, Poedjirahajoe, Handayani NSN, Hadisusanto S. 2019. The intertidal gastropods (Gastropoda: Mollusca) diversity and taxa distribution in Alas Purwo National Park, East Java, Indonesia. Biodiversitas 20: 2016-2027. Gastropods play an essential role in the ecosystem and can be used as bioindicators of environmental pollution. Understanding of their behavior, habitat, and distribution, and how these factors evolve, is crucial. This paper aimed to describe the diversity of the gastropod community and their spatial taxa distribution, based on the specimen frequency across all observed samples, in the diverse environment of Alas Purwo National Park (APNP), East Java, Indonesia. We studied eight beaches and two mangroves areas, and the study areas of the intertidal zone divided into upper, middle, and lower zones towards the sea. The purposive sampling was used to determine the locations and multi-plot quadrats for observations. The diversity of gastropods was elucidated by using the Shannon and Simpson indexes, while the Morisita index was applied for analyzing their spatial distribution pattern. However, the correspondence analysis and principal component analysis were performed using the software of PAST 3.22 for describing the diversity profile and individual rarefaction of gastropods together with environmental quality. There were three beach types: rocky, sandy, and muddy beaches were found in APNP. The highest diversity index (H’) was found on Pancur beach: H’ = 3.271, D = 0.947 of 67 species. The spatial distribution pattern of gastropods species was weakly clumped to random, with Ip: 0.165 - 0.016. Gastropods, both predators and scavengers, were distributed from the upper to lower zones. The distribution of gastropods in APNP is mostly in type B. These results expand our knowledge of gastropods diversity and distribution of Indonesia’s beach and can contribute to the future environmental assessments of biodiversity of tropical intertidal zones worldwide.

Gastropods Community in Babura River, Medan city

Gastropods communityin the Baburariverat Medan City were collected at Medan Johor and Medan Kota which consisted of 6 species of 96 ind., i.e. (1) Pomacea canaliculata [36 ind.], (2) Filopaludina javanica [5 ind.], (3) Lymnaea rubiginosa [2 ind.], (4) Tarebia granifera [11 ind.], (5) Melanoides tuberculata [35 ind.], and (6) Thiara scraba [7 ind.]. Total abundance was 39.0 ind./m2 in Medan Johor and 43.6 ind./m2 in Medan Kota. Diversity index (H’) was 0.897 in Medan Johor and 0.986 in Medan Kota, classified as low diversity and severe, equitability index (E) was 0.557 in Medan Johor, classified as moderate uniform and 0.711 in Medan Kota, classified as high uniform. Dominance index (C’) was 0.500 in Medan Johor and 0.463 in Medan Kota, both of which are moderately dominant. Gastropods were found to be influenced by physico-chemical parameters of water. The parameters which still supported gastropods life,i.e: temperature, turbidity, depth, pH, DO, and BOD, in contrary to strong velocity, nitrate, and phosphate.Our results then may reflect the preliminary data on gastropods assemblage in Babura river to enrich future data regarding gastropod communities in other study sites.

Gastropod Diversity in Mangrove Forests of Mojo Village, Ulujami District, Pemalang Regency, Indonesia

The development of mangrove ecosystem has a significant impact on fishery resources, such as gastropod. This research aimed at studying the community structure of mangrove forest in Mojo village, to identifying and analyzing the composition and diversity of gastropod, and investigating the effect of mangrove community on the abundance and gastropod. The research was conducted in Mojo Village, Ulujami District, Pemalang Region from November to December 2017. Identification of species and density was conducted on mangrove species by means of line and plot transects, while the gastropod was sampled from the field then identified in the laboratory. Three sampling stations were occupied in the data collection. The data analysis was conducted for diversity indices, including heterogeneity and evenness both for mangrove and gastropod. Statistical data analysis was conducted by regression to analyze the effect of mangrove density on the abundance of gastropod. The result showed that only three mangrove species were found in Mojo village, including Rhizophora mucronata, Avicennia marina and A. officinalis. Eight gastropod species were identified from mangrove forest of Mojo village. The most dominant gastropod species was Telescopium telescopium, followed by Cerithidea cingulata. The analysis of heterogeneity index showed a low value for mangrove community and medium value for the gastropod community, ranging from 0.353 to 0.720 and 1.462 to 1.812, respectively. Statistical data analysis showed that the density of R. mucronata and A. marina had a significant effect on the abundance of gastropod specieses, including Cerithidea quadrata and Casidula nucleus, both of which had logarithmic relationship trends.

The oldest members of Porcellioidea (Gastropoda): a new link between Baltica and Perunica

AbstractThe strata of Gotland, Sweden, provide one of the richest records of Silurian gastropod faunas in the world. Recent re‐evaluation of museum collections revealed for the first time the presence of gastropods of the superfamily Porcellioidea (Archaeogastropoda) in the Silurian strata of Gotland (Baltica). Additionally, the porcellioideans from Gotland represent the oldest record of the superfamily, members of which were an element of marine gastropod communities from Silurian to Cretaceous time, a period of more than 350 million years. The morphology of the sinistrally coiled teleoconchs in the oldest porcellioidean gastropods supports an existing hypothesis that the pseudo‐bilaterally symmetrical teleoconch and the mid‐whorl position of the selenizone in the post‐Silurian porcelliids is a derived shell character. The occurrence of porcellioidean gastropods in the Silurian strata of Baltica also represents a new faunal link between Baltica and Perunica which corresponds well with published palaeobiogeographical and palaeogeographical models. Six taxa are described, including the Sheinwoodian (early Wenlock) Gotlandiela contraria (Lindström), the Gorstian (early Ludlow) Mannegaardina hedei gen. et sp. nov., the Ludfordian (late Ludlow) Gotlandiela sp. and Pernericirrus lindstroemi sp. nov., as well as two agnesiid species.

Analysing the Role of Environmental Stresses on Species Richness and the Process of Hierarchical Structuring of Species Abundances in Marine Gastropods communities at Suva (Fiji Islands)

Anthropogenic environmental stresses, especially physio-chemical pollution, are causing steadily increasing threat to many ecosystems, among which coastal marine communities in tropical shallow waters are especially sensitive. In particular, species-rich marine gastropod assemblages are doomed to bear sharp drops in species diversity when exposed to pollutants released offshore. Yet, the details of the process of decline in species diversity remain to be addressed and analysed more deeply. By addressing a series of previously reported inventories of marine gastropod communities along a sharp gradient of pollution along southern coast at Suva (Fiji Archipelago), I first confirm the already recognised trend towards both a severe decrease in species richness and a strong increase of the unevenness in species abundance distribution, as a response to incremental pollution. Yet, the last trend – increased unevenness – reveals being essentially the purely mathematical consequence of the concomitant decline in species richness. In fact, the genuine intensity of the process of hierarchical structuring of species abundances proves remaining virtually unaffected by environmental degradation, contrary to what has been generally thought so far. Also, another unexpected aspect of the decline in species richness with growing pollution is that this decline is far from being primarily restricted to the set of rarest species; in fact, the originally abundant species are also largely implied in this decline.
 Moreover, considering separately the two co-occurring feeding guilds, it is shown that herbivores and carnivores are substantially involved the same in the drop in species diversity; as a result, their relative contributions in the community do not seem markedly contrasted by growing pollution. In another respect, a recently proposed paradigmatic hypothesis is supported, according to which the herbivore-guild has quite less numerous species with more unevenly distributed abundances, as compared to the carnivore-guild. Yet, once again, this increased unevenness is essentially the purely mathematical consequence of the concomitant decline in species richness; the genuine intensity of the process of hierarchical structuring of species abundances does remain substantially unchanged. At last, a comparatively extremely high sensitivity to pollution is highlighted for the emblematic genus Conus, which suffers, here, a dramatic drop in species diversity.

Gastropod communities associated with different morphologies of the intertidal seaweed Hormosira banksii

Hormosira banksii is an important intertidal habitat-forming seaweed in southern Australia that shows large variation in morphology. We examined the relationship between morphological variation in Hormosira and associated gastropod community structure, abundance and diversity in Tasmania, southern Australia. We sampled both Hormosira and gastropods from sites in two habitats (coast and estuary), two times (February–March and October–November) at two regions (northern and eastern Tasmania). There were distinct Hormosira morphs on the north coast (small individuals), east coast (intermediate sized individuals) and in estuaries (large individuals). Multivariate analysis showed that gastropod communities varied among the different algal morphologies, and suggest an influence of morphological traits, specifically thallus length, vesicle number and size, on the distribution patterns of gastropod species. Despite the finding of distinct gastropod communities associated with the different Hormosira morphs, because the different morphs occur in different locations with different physical conditions, we cannot unequivocally attribute the differences in gastropod communities to seaweed morphology per se. Nonetheless, our results confirm that H. banksii is an important foundation species in the intertidal zone and suggest a habitat-specific effect of algal morphological traits on gastropods.

Numerical Extrapolation of the Species Abundance Distribution Unveils the True Species Richness and the Hierarchical Structuring of a Partially Sampled Marine Gastropod Community in the Andaman Islands (India)

Even when it remains substantially incomplete, the partial inventory of a species assemblage can provide much more information than could be expected at first. This can be achieved by applying a rigorous numerical extrapolation procedure that fully extends the incomplete sampling in numerical terms and, thereby, provides reliable estimates regarding not only the number but also the distribution of abundances for the whole set of the undetected species. As a result, this makes available the full range of the Species Abundance Distribution of the yet partially sampled assemblage and, thus, allows to address a series of interesting issues regarding the process and pattern of the hierarchical structuring of species abundances within the studied assemblage of species. Moreover, the same kind of numerical extrapolation may be applied separately to each subset of species, within the whole assemblage, that may have relevant interest (taxonomic subgroups, feeding guilds, etc…). Thus, deconstructing the Species Abundance Distribution can provide further detailed insights into the functional organisation of the studied assemblage. The mathematical and algorithmic basis for this extrapolating procedure has been developed recently, to be applied to the numerical extension of both the Species Accumulation Curve and the Species Abundance Distribution. The wide potential interest of this new methodological approach, when having to deal with substantially incomplete inventories of species (which is doomed to become inevitable with increasingly species-rich assemblages), is illustrated by a detailed case study of a marine gastropod assemblage on rocky shore under tropical climate.

Land Snail Communities in Limestone Gorges from the Southern Part of the Metaliferi Mountains (Apuseni Mountains, Romania)

Abstract This study focuses on terrestrial gastropod communities in a karst area, where the presence of water and the limestone generates favourable environment for land snails. Three limestone gorges were analysed located in the southeast of the Metaliferi Mountains. Four different habitats in three limestone gorges were analysed – Glodului, Cibului and Mada. A total of 42 species of land snails were identified. The terrestrial gastropod communities in the area are dominated by calciphile species, such as Granaria frumentum, Truncatellina cylindrica and Alopia bielzii madensis. The differences between the analysed habitats are not pronounced enough to be reflected in the structure of the snail communities. Significant positive correlation was found between the abundance of land snails and the habitat exposure.

Structure of gastropod communities at mangrove ecosystem in Lubuk Kertang village, West Berandan District, Langkat Regency, North Sumatera Province

Gastropod was one of the class from mollusca in mangrove ecosystem. Lubuk Kertang Village’s mangrove forest was been converted into tourist areas, agricultural land and settlements. The purpose of this study was to analyze the structure of gastropods at Avicennia lanata, Rhizophora apiculata and Sonneratia alba. This research was conducted at Lubuk Kertang Village in February-March 2017. Gastropod were collected in 1 m × 1 m transect in mangrove. Examples of biota were taken by using shovel, then the biota was inserted into a plastic bag sample, wrote date of sampling and identified. The results showed there were 15 species Gastropods, namely Achatina fulica, Cerithidea alata, Cerithidea cingulata, Cerithidea obtusa, Chicoreus capucinus, Cymatium pileare, Ellobium aurimisdae, Ellobium aurisjudae, Littoraria melanostoma, Littoraria scabra, Murex tribulus, Nerita balteata, Nerita planospira, Pugilina cochlidium, Stramonita gradata, Telescopium telescopium and Terebralia sulcata. Diversity index ranged 1.702 to 2.165 was in medium category, Similarity index ranged 0.676 to 0.799 was in low category and Dominance index ranged 0.142 to 0.282 that categorized was low. The highest gastropod density was 31 individuals/m2 in the Sonneratia alba. The conclusion of the research is the existing mangrove ecosystem in Lubuk Kertang Village in a stable state.

STRUKTUR KOMUNITAS DAN DISTRIBUSI TEMPORAL GASTROPODA DI DANAU SITU GINTUNG, TANGERANG SELATAN, BANTEN

The changes in the physicochemical of waters in the lake ecosystem caused by seasonal variation, anthropogenic and industrial wastes impact the gastropod community. This study aimed to determine the physicochemical parameter of waters, community structure and distribution of gastropod, and the correlation between those two in the dry and rainy seasons. We conducted this research in the lake of Situ Gintung located in Tangerang Selatan, Banten, Indonesia during the dry season (May to August 2015) and the rainy season (February to April 2016). Statistical analysis showed the physicochemical parameter of waters in both seasons has no different, while the gastropod showed a slight difference in occurrence based on the season, in which rainy season had the highest occurrence. Canonical Correspondence Analysis (CCA) suggested that gastropods occurrence were affected by the light intensity in the rainy season and the temperature in the dry season.

Acidic, neutral and alkaline forest ponds as a landscape element affecting the biodiversity of freshwater snails

In recent years, the number of areas remaining under the influence of acidity has increased. At all levels of ecosystems, biodiversity decreases with acidification, due to the elimination of species that are most sensitive to low pH. Forest ponds belong to a specific group that varied in location, a huge amount of leaf litter, and isolation from other aquatic environments. They are crucial in the industrial landscape with well-developed industry and human activity. The aim was to investigate the relative importance of water chemistry in explaining snail assemblage compositions and species richness in forest ponds of contrasting pH. Patterns in gastropod communities were determined from an analysis in 26 forest ponds with multivariate gradient analysis. Ponds ranged in a base mean pH from 3.0 to 9.0. pH has been found to be an important factor influencing gastropod fauna. Neutral ponds support diverse communities, typical of small water bodies. In two acidic pond types, snail fauna was different. Among the species characteristic for acidic ponds (pH < 6) were Anisus spirorbis and Aplexa hypnorum. The greatest distinct characterised alkaline ponds with the numerous appearance of alien Physa acuta. The most diverse gastropod fauna was found in neutral ponds, whereas the lowest degree of diversity was found in ponds with the lowest pH. Current knowledge of pH-associated changes in aquatic ecosystems is still incomplete because anthropogenic acidification is a recent phenomenon. It is extremely important in forest habitats, since they react more intensively to climatic factors and are often used in landscape management and planning.

Conservation at a slow pace: terrestrial gastropods facing fast-changing climate.

The climate is changing rapidly, and terrestrial ectotherms are expected to be particularly vulnerable to changes in temperature and water regime, but also to an increase in extreme weather events in temperate regions. Physiological responses of terrestrial gastropods to climate change are poorly studied. This is surprising, because they are of biodiversity significance among litter-dwelling species, playing important roles in ecosystem function, with numerous species being listed as endangered and requiring efficient conservation management. Through a summary of our ecophysiological work on snail and slug species, we gained some insights into physiological and behavioural responses to climate change that we can organize into the following four threat categories. (i) Winter temperature and snow cover. Terrestrial gastropods use different strategies to survive sub-zero temperatures in buffered refuges, such as the litter or the soil. Absence of the insulating snow cover exposes species to high variability in temperature. The extent of specific cold tolerance might influence the potential of local extinction, but also of invasion. (ii) Drought and high temperature. Physiological responses involve high-cost processes that protect against heat and dehydration. Some species decrease activity periods, thereby reducing foraging and reproduction time. Related costs and physiological limits are expected to increase mortality. (iii) Extreme events. Although some terrestrial gastropod communities can have a good resilience to fire, storms and flooding, an increase in the frequency of those events might lead to community impoverishment. (iv) Habitat loss and fragmentation. Given that terrestrial gastropods are poorly mobile, landscape alteration generally results in an increased risk of local extinction, but responses are highly variable between species, requiring studies at the population level. There is a great need for studies involving non-invasive methods on the plasticity of physiological and behavioural responses and the ability for local adaptation, considering the spatiotemporally heterogeneous climatic landscape, to allow efficient management of ecosystems and conservation of biodiversity.

Spatial structure of a gastropod community in the litter of a beech forest of dentario-glandulosae fagetum in the Tatra Mountains

Spatial structure of a gastropod community in the litter of a beech forest of dentario-glandulosae fagetum in the Tatra Mountains

Impact assessment of intense sport climbing on limestone cliffs: Response of rock-dwelling land snails

Exposed limestone cliffs in the Swiss Jura Mountains harbour a diverse gastropod community with some rare species. Sport climbing has recently increased in popularity on these cliffs. We examined the effects of sport climbing and microtopographical features of rock faces on terrestrial gastropods by assessing species diversity and abundance on climbing routes and in unclimbed areas of seven isolated cliffs in the Northern Swiss Jura Mountains. We considered exclusively living individuals resting attached to rock faces. In total, 19 gastropod species were recorded. Six of them were specialized rock-dwelling species, whose individuals spend their entire life on rock faces, feeding on algae and lichens. Plots along climbing routes harboured fewer species of rock-dwelling snails as well as other gastropod species (usually living in the leaf litter layer at the cliffs’ base) than plots in unclimbed control areas. Similarly, both the density of individuals and frequency of occurrence in plots were reduced in both groups of snails on climbing routes. The complexity of the rock surface had little influence on the species richness and abundance of gastropods. Pyramidula pusilla, the species with the smallest shell and a preference to rest underneath overhangs, was less affected by sport climbing than snail species with larger shells and a preference to rest on exposed smooth rock surface. Our findings indicate land snail diversity and abundance are suitable indicators for impact assessment in rocky habitats. Future management plans and actions should therefore not only rely on plants; they ought to consider also gastropods and other invertebrates. Any management plan should include a comprehensive information campaign to show the potential impact of intensive sport climbing on the specialized flora and fauna with the aim of educating the climbers and increasing their compliance with such measures.

Beginning of a new age: How did freshwater gastropods respond to the Quaternary climate change in Europe?

Abstract The well documented fossil record of European Quaternary freshwater gastropods offers a unique resource for continental-scale biogeographical analyses. Here, we assembled a dataset including 338 freshwater gastropod taxa from 1058 localities across Europe, which we used to explore how freshwater gastropod communities varied in space and time across six distinct time intervals of the Quaternary, i.e. Gelasian, Calabrian, Middle Pleistocene, Last Interglacial, Last Glacial and Holocene. We took into consideration both species richness and qualitative structural patterns, comparing turnover rates between time intervals and examining variations in community nestedness-segregation patterns. Species richness differed significantly between time intervals. The Early Pleistocene showed the highest diversity, likely because of the contribution of long-lived aquatic systems like the lakes Bresse and Tiberino that promoted speciation and endemism. The rich Middle to Late Pleistocene and Holocene assemblages were mostly linked to fluvial and/or lacustrine systems with short temporal durations. We identified a major turnover event at the Plio-Pleistocene boundary, related to the demise of long-lived lakes and of their rich, endemic faunas at the end of the Pliocene. In the subsequent intervals, little or no turnover was observed. We also observed a pattern of high segregation in Early Pleistocene communities, associated with the abundance of endemic species with small distribution ranges, and reflecting the provincial character of the aquatic freshwater systems at that time. This structured pattern disintegrated gradually towards the Middle Pleistocene and remained unstructured up to present. In particular, spatial patterns of community nestedness-segregation in the Last Interglacial and Holocene suggest a random recolonization of freshwater habitats mostly by generalist species following deglaciation.

Assembly processes of gastropod community change with horizontal and vertical zonation in ancient Lake Ohrid: a metacommunity speciation perspective

Abstract. The Balkan Lake Ohrid is the oldest and most diverse freshwater lacustrine system in Europe. However, it remains unclear whether species community composition, as well as the diversification of its endemic taxa, is mainly driven by dispersal limitation, environmental filtering, or species interaction. This calls for a holistic perspective involving both evolutionary processes and ecological dynamics, as provided by the unifying framework of the “metacommunity speciation model”.The current study used the species-rich model taxon Gastropoda to assess how extant communities in Lake Ohrid are structured by performing process-based metacommunity analyses. Specifically, the study aimed (1) to identifying the relative importance of the three community assembly processes and (2) to test whether the importance of these individual processes changes gradually with lake depth or discontinuously with eco-zone shifts.Based on automated eco-zone detection and process-specific simulation steps, we demonstrated that dispersal limitation had the strongest influence on gastropod community composition. However, it was not the exclusive assembly process, but acted together with the other two processes – environmental filtering and species interaction. The relative importance of the community assembly processes varied both with lake depth and eco-zones, though the processes were better predicted by the latter.This suggests that environmental characteristics have a pronounced effect on shaping gastropod communities via assembly processes. Moreover, the study corroborated the high importance of dispersal limitation for both maintaining species richness in Lake Ohrid (through its impact on community composition) and generating endemic biodiversity (via its influence on diversification processes). However, according to the metacommunity speciation model, the inferred importance of environmental filtering and biotic interaction also suggests a small but significant influence of ecological speciation. These findings contribute to the main goal of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) deep drilling initiative – inferring the drivers of biotic evolution – and might provide an integrative perspective on biological and limnological dynamics in ancient Lake Ohrid.

New gastropod assemblages from the Early/Middle Miocene of Riedensheim and Adelschlag-Fasanerie, southern Germany

This work presents a taxonomic study and paleoecological reconstructions of the continental gastropod assemblages from two new Miocene localities in the German part of the North Alpine Foreland Basin, Bavaria. Riedensheim (next to the town of Rennertshofen) and Fasanerie (next to the town of Adelschlag). The fossil rich deposits belong to the Upper Freshwater Molasse (OSM), correlated to the regional biostratigraphic unit C+D (Burdigalian/Langhian;MN 5 in the European mammal Neogene zone). 17 gastropod species (almost exclusively pulmonates) were found in Adelschlag-Fasanerie and 35 species in Riedensheim. 13 species are shared by both assemblages. Of these, the following species have their distribution expanded in Germany: Azeca peneckei, Carychium (Carychium) galli, Vitrea ammoni and Urticicola perchtae;and possibly also Stagnicola cf. praebouiletti and Truncatellina cf. pantherae. Paleoecological reconstructions indicate a rich freshwater gastropod community in Riedensheim, with a well-vegetated area immediately surrounding the water body (which diminished in size with time), and a surrounding environment dominated by humid forest. The fauna from Adelschlag-Fasanerie, which was much impoverished in comparison, might represent flood plain and fluvial channel deposits. Finally, a comparison to the molluscan faunas of coeval and nearby localities (Adelschlag, Attenfeld, Sandelzhausen and Undorf) is provided.

Observations and Experiments on the Biology and Life History of Riseriellus occultus (Heteronemertea: Lineidae).

Studies on the biology and life history of nemerteans are scarce, mostly because these animals are nocturnal. In order to broaden the knowledge base on the life history of nemerteans as a prerequisite for comparative analyses, we studied a population of Riseriellus occultus (Heteronemertea: Lineidae) inhabiting the rocky intertidal in southern Brittany near Concarneau (France) for more than 10 years. Our studies show that R. occultus is an iteroparous, perennial species exclusively inhabiting rocky shore crevices that result from onionskin weathering of the granite. From September through October R. occultus reproduces by external fertilization and develops via a planktonic pilidium larva, which, under laboratory conditions, metamorphoses after about six weeks. Adults of R. occultus are nocturnal macrophagous predators that preferentially feed on the gastropods Gibbula umbilicalis and Patella species, but also consume the bivalve Mytilus edulis. Since R. occultus devours the snail inside the shell, we fixed individuals while feeding, and serially sectioned them. Reconstruction of the sections shows that R. occultus swallows the entire soft body and finally detaches the columellar muscle from the shell. Estimates on the density of R. occultus inside the rock crevices provide evidence for clustered distribution and locally high abundance on the rocky shore. These data strongly suggest that R. occultus affects the structure of the rocky shore gastropod community. Although our data are still fragmentary with respect to the ecology of this species and its role in the local food web, our knowledge has grown to such extent that R. occultus can now be regarded as one of the few well characterized nemertean species.