Endemic Gastropod Research Articles

Co-introduction into a delicate island ecosystem: metastrongyloid nematodes (superfamily Metastrongyloidea) of veterinary and medical importance circulating in aquatic and terrestrial environments of Tenerife (Canary Islands).

Metastrongyloid nematodes typically reside as adults in the cardiopulmonary systems of their mammalian definitive hosts, potentially causing severe diseases. Of particular concern are Angiostrongylus cantonensis and A. costaricensis, which can cause eosinophilic meningitis and abdominal angiostrongyliasis, respectively, in their accidental human hosts. Several metastrongyloid species of medical and veterinary importance have been documented in the Canary Islands. However, the gastropod species acting as intermediate hosts for some of these nematodes in the archipelago remained unknown. This study aimed to investigate the occurrence of metastrongyloid nematodes in terrestrial and aquatic gastropods, including both endemic and non-native species, on Tenerife. Foot samples from terrestrial and aquatic gastropods were analyzed using a multiplex PCR targeting the Internal Transcribed Spacer 1 (ITS1), allowing the specific detection of A. cantonensis, A. vasorum, Aelurostrongylus abstrusus, Crenosoma striatum, Troglostrongylus brevior, and Crenosoma vulpis. Five metastrongyloid species, namely C. striatum, A. cantonensis, Ae. abstrusus, A. vasorum, and an unidentified metastrongyloid, were identified within both non-native and endemic terrestrial gastropods. In the aquatic snail Physella acuta, only A. cantonensis and C. striatum were detected. This study confirms the introduction of various metastrongyloids associated with non-native mammalian fauna and provides new data on the occurrence of these nematodes in non-native and endemic gastropod species, including their presence in aquatic environments on the Canary Islands.

Assessing phenotypic variation and plasticity of endemic gastropods from thermal water refugia using complex morphometric techniques: A case study of Lake Pețea melanopsids.

Understanding the underlying reasons for phenotypic plasticity and resulting morphological disparity is one of the key topics of evolutionary research. The phenotypic plasticity of extant and fossil melanopsids has been widely documented. Yet millennial-resolution, well-dated records from small aquatic habitats harboring endemics are scarce. The thermal spring-fed Lake Pețea is an ice age refugia harboring a unique endemic warm-water fauna. Subfossil melanopsids display incredible morphological variability from smooth to keeled, elongated to ribbed, shouldered forms. Numerous morphotypes have been considered as individual taxa with a fluent succession from the smooth elongated to the ribbed, shouldered types. This study presents an extensive morphometric analysis of subfossil melanopsids (ca. 3500 specimens) derived from stratified samples with an independent chronology. The aim was to separate morphotypes for investigations of temporal morphological disparity. Our results challenge the widely accepted hypothesis that proposes the evolution of shouldered, compressed, ribbed shells through a two-step process from smooth elongated spindle-shaped shells. Instead, it suggests that the subfossil shells belong to two distinct taxa present throughout the available stratigraphic data. The main components of shape variation, shape globularity, and shell coiling seem allometry-related. Ribs, striation, and keels appear randomly. High-spired spindle-shaped forms were considered to represent specimens of Microcolpia daudebartii hazayi. Bulkier low-spired and shouldered specimens represent phenotypes of Mi. parreyssii parreyssii. The collective and random distribution of morphotypes from the early stages of the lake's history also refutes the idea of a continuous transformation of the elongated forms into compressed, shouldered ones. Rather points to multiple events and environmental stimuli triggering development. Melanopsids appear in Late Glacial horizons, with Theodoxus prevostianus preferring temperatures above 23°C which may indicate the subordinate presence of hot water microhabitats in cooler waters.

Coordinated response of endemic gastropods to Late Glacial and Holocene climate-driven paleohydrological changes in a small thermal pond of Central Europe

The thermal spring-fed Lake Pețea located in NW Romania southeast of the city of Oradea harbors a unique endemic warm water biota. It is the only location in Europe where thermal water endemic melanopsid Microcolpia parreyssii (Philippi, 1847) lived along with the highly endangered warm-water relict neritid Theodoxus prevostianus. Lake Petea’s evolution was mainly controlled by major climate-driven hydrological changes also seen in regional records. The hydrological changes were mainly controlled by varying input of thermal water due to recurring increased/decreased recharge of the underground karst water system. The driving factor was warming connected to the interstadial GI 1 increasing recharge by melting of regional ice sheets in the Late Glacial. Conversely, during the Younger Dryas (H0) and the Holocene increasing/decreasing moisture availability was in control. Low stands created multiple bottlenecks reducing genetic variability seen in the appearance of extreme morphologies during next rapid climate melioration. The studied gastropods responded mostly similarly to changes controlling the availability of elements in shell construction and habitat reduction leading to changes in shape, density, size. Periods of lower lake levels and reduced warm water input are characterized by the emergence of elongated tightly coiled shells while globular, compressed loosely coiled shells develop at times of warmer water provision and increased Mg availability. In size there is a contrasting trend. Namely globose Th. prevostianus shells are larger than the elongated ones. Conversely globose, compressed Microcolpia are generally smaller than their elongated spindle-shaped counterparts. In this sense the development of dwarf morphotypes in warmer water habitats is characteristic of Lake Pețea melanopsids. This type of dwarfism i.e. the reduction of shell size is lacking though in Lake Pețea neritids. Our findings also confirm the presence of various ecophenotypes of Microcolpia in the pond degrading our endemic species Mi. parreyssii to a variety of Mi. daudebartii.

Isotopes suggest trophic differences between alien Radix auricularia (Linnaeus, 1758) (Lymnaeidae) and sympatric endemic gastropods in Lake Baikal

Isotopes suggest trophic differences between alien Radix auricularia (Linnaeus, 1758) (Lymnaeidae) and sympatric endemic gastropods in Lake Baikal

The biocontrol nematode Phasmarhabditis hermaphrodita infects and increases mortality of Monadenia fidelis, a non-target terrestrial gastropod species endemic to the Pacific Northwest of North America, in laboratory conditions.

Inundative biological control (biocontrol) efforts in pest management lead to the mass distribution of commercialized biocontrol agents. Many 'biocontrol gone awry' incidents have resulted in disastrous biodiversity impacts, leading to increased scrutiny of biocontrol efforts. The nematode Phasmarhabditis hermaphrodita is sold as a biocontrol agent on three continents and targets pest gastropods such as Deroceras reticulatum, the Grey Field Slug; P. hermaphrodita is not presently approved for use in the United States. Investigations into the potential for P. hermaphrodita to infect non-target gastropod species of conservation relevance, however, are limited. We examined the effects of three strains of P. hermaphrodita on mortality in Monadenia fidelis, the Pacific Sideband, a snail species endemic to the Pacific Northwest of North America, in laboratory conditions. Across a 71-day laboratory infectivity assay, snails exposed to each of the three nematode strains, each analyzed at two doses, experienced a mean 50% mortality by days 20-42. All nematode-treated snails were dead by the end of the study. By contrast, 30/30 water-control snails experienced no mortality. Nematodes killed smaller, juvenile-stage snails significantly faster than those in larger and more developmentally advanced hosts. Our results provide direct evidence that the biocontrol nematode P. hermaphrodita infects and kills M. fidelis, a non-target gastropod species endemic to the Pacific Northwest, in laboratory conditions. This study suggests that introduction of P. hermaphrodita to new ecosystems might negatively impact endemic gastropod biodiversity and advocates for further investigation of non-target effects, including in conditions closer to the natural environments of non-target species.

To be alive or not to be alive: Radiocarbon data provide new perspective on species diversity in the Caspian Sea

Abstract The Caspian Sea is undergoing a severe biodiversity crisis. However, estimates of current extinction rates are difficult to obtain due to the lack of reliable pre‐Anthropocene baseline data. For example, because the majority of endemic gastropod species was described from “fresh looking” shells, it remains unclear which species still existed prior to the Anthropocene. This study therefore used the species‐rich microgastropod family Hydrobiidae to assess the extent to which endemic species were collected alive during the Anthropocene. Literature and database searches were performed. In addition, 14C dating was conducted on “fresh looking” shells collected in the Caspian Sea during the last 150 years. The literature review revealed that 75% of the “recent” species are only known from empty shells and 25% were recorded with a soft body. The 14C data showed that all “recent” specimens examined had an age between 1624 cal BC and 1888 cal AD. Two species studied predate the beginning of the Anthropocene. Two other species potentially or likely existed during the Anthropocene. This suggests that the number of endemic species still present at the beginning of the Anthropocene is lower than previously thought. The data also suggest that there was a substantial loss of species between the late 18th century and the 1950s and that only two endemic hydrobiid species have recently been found alive. These findings further contribute to the notion of a severe biodiversity crisis in the Caspian Sea. For accurate estimates of current extinction rates of Caspian Sea gastropods, pre‐Anthropocene biodiversity data need to be further corroborated. Particularly, studies are required to clarify the taxonomic status of the dubious taxa and a possible “collection crisis” in the Caspian Sea due to decreasing sampling efforts in recent decades. In addition, comprehensive IUCN assessments are urgently required.

Viral Diversity in Samples of Freshwater Gastropods Benedictia baicalensis (Caenogastropoda: Benedictiidae) Revealed by Total RNA-Sequencing.

Previously, the main studies were focused on viruses that cause disease in commercial and farmed shellfish and cause damage to food enterprises (for example, Ostreavirusostreidmalaco1, Aurivirus haliotidmalaco1 and Aquabirnavirus tellinae). Advances in high-throughput sequencing technologies have extended the studies to natural populations of mollusks (and other invertebrates) as unexplored niches of viral diversity and possible sources of emerging diseases. These studies have revealed a huge diversity of mostly previously unknown viruses and filled gaps in the evolutionary history of viruses. In the present study, we estimated the viral diversity in samples of the Baikal endemic gastropod Benedictia baicalensis using metatranscriptomic analysis (total RNA-sequencing); we were able to identify a wide variety of RNA-containing viruses in four samples (pools) of mollusks collected at three stations of Lake Baikal. Most of the identified viral genomes (scaffolds) had only distant similarities to known viruses or (in most cases) to metagenome-assembled viral genomes from various natural samples (mollusks, crustaceans, insects and others) mainly from freshwater ecosystems. We were able to identify viruses similar to those previously identified in mollusks (in particular to the picornaviruses Biomphalaria virus 1 and Biomphalaria virus 3 from the freshwater gastropods); it is possible that picorna-like viruses (as well as a number of other identified viruses) are pathogenic for Baikal gastropods. Our results also suggested that Baikal mollusks, like other species, may bioaccumulate or serve as a reservoir for numerous viruses that infect a variety of organisms (including vertebrates).

Comparison of the evolutionary patterns of DNA repeats in ancient and young invertebrate species flocks of Lake Baikal.

DNA repeat composition of low coverage (0.1-0.5) genomic libraries of four amphipods species endemic to Lake Baikal (East Siberia) and four endemic gastropod species of the fam. Baicaliidae have been compared to each other. In order to do so, a neighbor joining tree was inferred for each quartet of species (amphipods and mollusks) based on the ratio of repeat classes shared in each pair of species. The topology of this tree was compared to the phylogenies inferred for the same species from the concatenated protein-coding mitochondrial nucleotide sequences. In all species analyzed, the fraction of DNA repeats involved circa half of the genome. In relatively more ancient amphipods (most recent common ancestor, MRCA, existed approximately sixty millions years ago), the most abundant were species-specific repeats, while in much younger Baicaliidae (MRCA equal to ca. three millions years) most of the DNA repeats were shared among all four species. If the presence/absence of a repeat is regarded as a separate independent trait, and the ratio of shared to total numbers of repeats in a species pair is used as the measure of distance, the topology of the NJ tree is the same as the quartet phylogeny inferred for the mitogenomes protein coding nucleotide sequences. Meanwhile, in each group of species, a substantial number of repeats were detected pointing to the possibility of non-neutral evolution or a horizontal transfer between species occupying the same biotope. These repeats were shared by non-sister groups while being absent in the sister genomes. On the other hand, in such cases some traits of ecological significance were also shared.

New data on the spawning of the Brazilian endemic gastropod Voluta ebraea (Mollusca: Volutidae)

New data on the spawning of the Brazilian endemic gastropod Voluta ebraea (Mollusca: Volutidae)

The lost vent gastropod species of Lothar A. Beck.

Deep-sea hydrothermal vents host many endemic species adapted to these chemosynthesis-based ecosystems. The exploration of vent fields including those in the tropical Pacific is currently accelerating, due to the development of deep-sea mining for valuable minerals. Molecular evidence has shown that many vent endemic gastropod lineages include sibling species pairs in adjacent oceanic basins. While the fauna of the Manus Basin is relatively well described, many lineages in adjacent regions in North Fiji or Lau Basins are recognised as separate species, but unnamed. Valuable material from this fauna was studied by Lothar A. Beck in the 1990s, who fully drafted descriptions for these species, but did not publish them. Beck's manuscript names, prior to the present study, represented real species but nomina nuda without taxonomic validity. Here we present the descriptions of seven new species and one new genus, extracted from Beck's unpublished manuscript that was rediscovered after his death in 2020. The publication of these descriptions makes them taxonomically available and respects the scientific contributions of Beck. Providing valid descriptions of these species is critically important now to enable the recognition of species that may require conservation in the face of future environmental destruction. Symmetriapelta Beck, gen. nov. is described as new genus. Bathyacmaea nadinae Beck, sp. nov., Pyropelta ovalis Beck, sp. nov., Pseudorimula leisei Beck, sp. nov., Lepetodrilus fijiensis Beck, sp. nov., Shinkailepas conspira Beck, sp. nov., Symmetromphalus mcleani Beck, sp. nov. and Symmetriapelta wareni Beck, sp. nov. are introduced as new species.

Integrating genetic and biophysical approaches to estimate connectivity in an isolated, insular system: case of the culturally important marine gastropod Monetaria caputdraconis

Abstract Population connectivity has a fundamental role in metapopulation dynamics with important implications for population persistence in space and time. Oceanic islands, such as Easter Island (EI) and the Salas & Gómez Island (SG), are ideal for the study of population connectivity because they are separated by 415 km and isolated from other islands in the Pacific Ocean by >2000 km. Considering that the dispersal process could play a critical role in the persistence of their populations, we evaluated the connectivity pattern of the endemic gastropod Monetaria caputdraconis between EI and SG using population genetics and biophysical modelling. Eleven microsatellite loci did not show differences in the allelic frequency of individuals located in EI and SG, suggesting the presence of one genetic population. Historical reciprocal migration implies that 0.49% of the recruits in EI come from SG and 0.37% in SG come from EI. Considering year-round larval release and a larval development of 2 weeks in the plankton, a Lagrangian experiment based on a regional oceanic simulation indicated a weak population connectivity with a high rate of self-recruitment. Interestingly, self-recruitment showed both monthly and interannual variation ranging from 1 to 45% of returned larvae, with lower values estimated in SG compared to EI. The results suggest that few larvae/individuals arrive at each other's island, possibly due to stochastic events, such as rafting. Overall, our results indicate that both islands maintain population connectivity despite their distance; these findings have implications for designing conservation strategies in this region.

Population structure and demographic history of the gastropod Thaisella chocolata (Duclos, 1832) from the Southeast Pacific inferred from mitochondrial DNA analyses.

The present‐day population structure of a species reflects the combination of oceanographic currents, life‐history traits, and historical events. However, little is known about the mechanisms that have shaped the gene lineage distribution of marine species inhabiting the Southeast Pacific. Here, we provide a comprehensive phylogeographical study of a species distributed along the Southeast Pacific coastal region by analyzing the endemic gastropod Thaisella chocolata (Duclos, 1832). Sequencing of mitochondrial cytochrome c oxidase subunit 1 (CO1) and 16S rRNA revealed strikingly high haplotypic nucleotide and genetic diversity but a lack of significant population differentiation within the survey area. In addition, a star‐shaped phylogeny and significantly negative Tajima's D and Fu's Fs tests of neutrality suggested historical occurrence of rapid demographic expansion. Mismatch distributions and Bayesian inference analyses also confirmed T. chocolata to have undergone two ancestral demographic expansions. Calculations suggested that these expansions began in the lower and middle Pleistocene epoch, likely due to continental shelf development and climatic conditions. These findings could help establish a genetic baseline for T. chocolata as the first step toward sustainable spatial management of this species, as well as understand this species’ response to future climate change.

Exploitation Drives Changes in the Population Connectivity of Queen Conch (Aliger gigas)

The queen conch, Aliger gigas, is an endemic and iconic marine gastropod of the Wider Caribbean region that has been harvested for thousands of years. Conch are slow-moving and require contact to mate; overfishing has reduced populations in many areas compromising its rates of reproduction. Long-range dispersal and mixing between distinct populations occur in the queen conch’s early life history stages, when pelagic larvae are transported by oceanic currents. Genetic studies suggest that gene flow between populations decreases as the distance between populations increases. Here, we assessed how the population connectivity of conch changes with spatially variable patterns of fishing exploitation by simulating larval dispersal and comparing the potential connectivity under an unexploited and a contemporary exploited reproductive scenario. Results demonstrate that reduced egg production, due to heterogeneous fishing pressure and localized depletion, significantly alters population connectivity patterns as well as the structuring of populations and metapopulations across the species’ range. This strongly suggests that estimates of contemporary demographic rates, together with estimates of reproductive output need to be included in population connectivity studies. The existence of self-sustained metapopulations of queen conch throughout the Wider Caribbean suggests that replenishment through larval dispersal occurs primarily within sub-regional spatial scales, emphasizing the need for regional and local conservation and management measures to build and protect reproductively active populations and nursery habitat across multiple jurisdictions.

The freshwater molluscs of Serbia: Annotated checklist with remarks on distribution and protection status.

We present a checklist of 86 valid freshwater mollusc species of Serbia (65 gastropods and 21 bivalves) belonging to 19 families (15 gastropods and four bivalves). The list is based on our latest research and includes data from published sources and personal communications. The most diverse family among gastropods is Planorbidae (16 species), while Sphaeriidae are most diverse within the bivalves (10 species). Ten species are local endemics (all of them gastropods), while eight are introduced species (three gastropods and five bivalves). The Danube River and its smaller tributaries harbour the most diverse gastropod community, with a total of 61 species (41 gastropods and 20 bivalves). The snail Theodoxus transversalis (Pfeiffer, 1828) and the bivalve Unio crassus Philipson, 1788 are listed as EN (endangered) on the global (IUCN) level, while the snail Plagigeyeria gladilini Kuer, 1937 and the bivalves Pseudanodonta complanata (Rossmssler, 1835) and Sphaerium rivicola (Lamarck, 1818) are considered as VU (vulnerable) species. Of those IUCN taxa, only U. crassus is listed as protected on the national level (along with 12 mostly local endemic gastropod species). In comparison with the previous checklist of gastropods by Karaman Karaman (2007), a total of seven species are added here: Belgrandiella serbica Gler 2008, Bythinella istoka Gler Pei 2014, B. nonveilleri Gler 2008, B. pesterica Gler 2008, Acroloxus lacustris (Linnaeus, 1758), Melanoides tuberculata (O.F. Mller, 1774) and Armiger crista (Linnaeus, 1758). In view of global and regional trends in taxonomy, ecology and invasive biology, an even richer diversity of the Serbian freshwater malocofauna can be expected.

Fortuitous insights into the ecology of a recently charted deep-sea hydrothermal vent, using snails’ feet

Here we present the results from a shotgun sequencing effort on foot tissues from a deep-sea hydrothermal vent endemic limpet. We present the complete mitochondrial genome of the hydrothermal vent endemic gastropod Peltospira smaragdina (Gastropoda, Peltospiridae) for the first time. This species is characteristic of circa-Azores hydrothermal vent ecoregion and provides a candidate environmental DNA (eDNA) indicator of active hydrothermal vent sites. The results also suggest that the epilithic biofilm on the newly discovered Moytirra hydrothermal vents is dominated by Sulfurimonas –like microbes and corresponds with similar studies on hydrothermal hosted microbial communities. The association between Peltospira and Sulfurimonas is presented as potentially a holobiontic relationship, with both the snail and the microbial biofilm. We highlight the efficacy of using non-traditional sampling to develop a broader ecosystem understanding.

How ancient is Lake Lugu (Yunnan, China)? The gastropods’ viewpoint with focus on Radix (Lymnaeidae)

Lake Lugu has been termed an “ancient lake” in several publications. Ancient lakes, such as Baikal or Tanganyika have in common an age of several million years and an outstanding biodiversity and rate of endemism. Lake Lugu’s age is unknown, however, and has been inferred from the presumed Pliocene increased tectonic activity on the Yunnan-Guizhou Plateau. The lake was thus considered to be of tectonic origin, but supporting studies do not exist. Here we report and describe seven endemic species. The endemic gastropod Gyraulus luguhuensis exhibits an aberrant pseudo-dextral shell morphology, which is predominantly known from undisputed ancient lakes. To better understand the origin of the lake and of its biodiversity, we present a preliminary geological study, which shows that Lake Lugu is a tectonic-solution lake. During a survey of the aquatic habitats up to 21 gastropod morphospecies could be differentiated macro-morphologically. An aberrant neritid-like Radix was genetically studied for the first time. The genetic data suggest that Lugu-Radix, typical and neritid shell shapes, constitute a clade, comprising four possibly endemic evolutionary lineages, which potentially represent four different species. The molecular-clock approach indicates a Late Pliocene to Early Pleistocene origin of the clade, which we consider the minimum age of Lake Lugu. Our study reveals that the biodiversity in general and that of gastropods in particular is significantly higher than previously known. Against this background and considering the co-occurrence of aberrant Gyraulus and Radix with an evolutionary history of more than two million years, Lugu is putatively an ancient lake.

Biophysical Habitat Features Explain Colonization and Size Distribution of Introduced Trochus (Gastropoda)

The trochid gastropod, Rochia nilotica is harvested in small-scale fisheries throughout Southeast Asia and the Pacific Islands, many of which were created from inter-country translocations. This species is found on structurally complex shallow reefs, but specific habitat requirements have not yet been quantified in order the maximize the success of future translocations and help future-proof the fishery in changing ocean conditions. At 28 sites around Samoa, where the species was introduced in the early 2000s, we measured a suite of habitat variables along transects in which R. nilotica were counted and the shell sizes measured in a parallel study. Boosted regression tree analyses revealed that R. nilotica were most abundant at reef locations that were shallow, with fairly consistent depth, high cover of branching coral, low cover of erect macroalgae, low wave exposure and high surface complexity. Smaller individuals were associated with wide reef flats and high cover of branching coral, whereas larger animals occurred in deeper water with high surface complexity. Multivariate analyses showed this species to be a habitat generalist, sharing much of its niche with an endemic herbivorous gastropod, Tectus pyramis. Future stocking programs should focus on sites with habitats optimal for both adults and juveniles. R. nilotica populations are likely to be especially affected by broadscale stressors that result in declines in live coral cover and substratum complexity and increasing coverage of macroalgae on coral reefs.

Lake Tanganyika endemic gastropods also occur in the Lukuga River

Ancient lakes with their endemic species assemblages, like Lake Tanganyika in East Africa, are regarded as hotspots of aquatic biodiversity and as natural laboratories providing insights into evolutionary processes, such as intra-lacustrine speciation. The origin of the gastropod species super flock in Lake Tanganyika has been debated intensively and remains unclear to date. For the fish community, it is generally assumed that it was derived from ancestors occurring in the Congo River Basin. Recently, a central biogeographical role of the Lukuga River system and the connected Lualaba River has been indicated. In an attempt to trace the origin of the enigmatic thalassoid gastropods of Lake Tanganyika, the fauna of the Lukuga-Lualaba systems is currently being studied. A recent expedition allowed collecting mollusc material from the eastern shores of Lake Tanganyika around Kalemie and down the Lukuga River until Niemba. We found gastropods known to be endemic to Lake Tanganyika living in the Lukuga River as far down as 95 km, in populations with reasonable abundances. Based on mitochondrial DNA sequences, these populations are partially genetically distinct from Lake Tanganyika’s populations. However, sister taxa to the species flock have not yet been found in the Lukuga River. Our results are discussed in the context of intra-riverine evolutionary dynamics over shorter time periods. They will also help to understand the biogeographical and evolutionary dynamics within a large spatial and temporal framework, covering Lake Tanganyika and the Congo River system.

Intraspecific genetic variation in gastropods Liobaikalia stiedae (Dybowski, 1875) in Baikal

Genetic variation of Baikal endemic gastropods Liobaikalia stiedae was analyzed using the nucleotide sequence of the COI mitochondrial gene fragment. High intraspecific mtDNA differentiation is revealed, while local populations can be more similar to related species than to other populations.

First Reports on the Bacterial Community of the Digestive System of Endemic Baikal Gastropods Benedictia baicalensis

Abstract—Diversity and comparative analysis of the microbiota composition of the digestive system of Lake Baikal endemic gastropods Benedictia baicalensis (Caenogastropoda) and of the bottom sediments from their habitat were studied. Strains belonging to 11 genera of heterotrophic bacteria (Pseudomonas, Acinetobacter, Alcaligenes, Flavobacterium, Enterobacter, Escherichia, Citrobacter, Klebsiella, Bacillus, Staphylococcus, Streptococcus, and Micrococcus) were isolated from the stomach and gut content. Molecular genetic analysis of total DNA from the digestive tract revealed the 16S rRNA gene sequences of the genera Pseudomonas, Flavobacterium, Mesorhizobium, Deefgea, and of the phylum Tenericutes. Most isolates were found to utilize various organic substances, including those of animal origin, which was probably due to the pantophagy of these mollusks. The cultured bacterial community of B.baicalensis digestive system was shown to be formed by gram-negative bacteria (95–97% strains), although in the bottom sediments 51% of the isolates were gram-positive coccoid and spore-forming rod-shaped bacteria. Low frequency of occurrence or complete absence of gram-positive bacteria in the mollusk intestine compared to the bottom sediments (fivefold or more) may indicate their use as a nutrient substrate.