Gastropod Fauna Research Articles

Idiopyrgus Pilsbry, 1911 (Gastropoda, Tomichiidae): a relict genus radiating into subterranean environments

The freshwater gastropod fauna in Brazil presently consists of circa 180 known species, though this is deemed an underestimate. The little-studied cavern faunas have been considered a potential source of undescribed species, particularly regarding the Truncatelloidea. Here, based on new collection efforts in caves in Bahia state, Brazil, we describe two new troglobitic species of Idiopyrgus (Tomichiidae): Idiopyrgus eowynaesp. nov. and Idiopyrgus meriadocisp. nov. We improve upon the previous molecular phylogeny of this genus and take the opportunity to reclassify Spiripockia umbraticola Simone & Salvador, 2021, as Idiopyrgus umbraticola (Simone & Salvador, 2021), comb. nov. The genus Idiopyrgus now contains ten species, reinforcing the presence of Tomichiidae in Brazil as a relict lineage that largely radiated into cave environments. Furthermore, considering that so far only snapshots of their biology are known, we have collated all the information currently available from the literature and field observations on the cavernicolous species of Idiopyrgus. Notably, due to human action in the area where the two new species have been found, they can already be considered vulnerable.

Rapid declines in freshwater gastropods in Pune city, India

ABSTRACT We studied freshwater gastropod fauna in a heavily urbanized region in tropical India, across a range of habitat types. A total of 16 species were found from a two-year survey, which is a decline of 27% compared to studies completed in the 1970s. Planorbidae was the most species rich family in the collection, with five species. Racesina luteola (Lamarck, 1822) was the most commonly occurring species in the collection. Three non-native species, including Pomacea diffusa (Blume, 1957), are also reported. Habitat type influenced species occurrences, although lentic and lotic habitats were largely similar in their fauna. Many species reported previously were missing from the current survey, along with an increased incidence of non-native species which were absent from earlier reports. This decline in species richness, particularly of native species, alongside an increased incidence and spread of non-native species in the region, highlights the impact of urbanization on the freshwater gastropod community.

New species and records of limpets (Mollusca, Gastropoda) from the Pacific Costa Rica Margin.

The ocean remains a reservoir of unknown biodiversity, particularly in the deep sea. Chemosynthesis-based ecosystems, such as hydrothermal vents and hydrocarbon seeps, host unique and diverse life forms that continue to be discovered and described. The present study focuses on patelliform gastropods (limpets) collected from Pacific Costa Rica Margin hydrocarbon seeps during three research cruises from 2017 to 2019. Genetic and morphological analyses revealed the presence of several new lineages within the genera Bathyacmaea Okutani, Tsuchida & Fujikura,1992, Cocculina Dall, 1882, Paralepetopsis McLean, 1990, and the family Lepetodrilidae McLean, 1988: Bathyacmaealevinae sp. nov., Paralepetopsisvariabilis sp. nov., Pseudolepetodriluscostaricensis gen. et sp. nov., and Cocculinamethana sp. nov. These investigations also expanded the known ranges of the species Pyropeltacorymba McLean, 1992 and Lepetodrilusguaymasensis McLean, 1988 to the Costa Rica Margin. This research highlights the uniqueness of gastropod fauna at the Costa Rica Margin and contributes to our understanding of the biodiversity at chemosynthesis-based deep-sea ecosystems in the face of global biodiversity loss and increased commercial interest in deep-sea resources.

The Central Paratethys Sea – Part of the tropical eastern Atlantic rather than gate into the Indian Ocean

The Miocene Paratethys Sea is frequently depicted as junction between the Proto-Mediterranean Sea and the Indian Ocean. Herein, we elucidate the biogeographic character of this large epicontinental Miocene sea based on its speciose gastropod fauna. We debunk the persistent myth that there was a connection between these marine realms during Langhian times via the Tethys Seaway. Throughout most of the Early and Middle Miocene the connectivity of the Central Paratethys was via the Rhône Strait and the Slovenian Strait as supported by up to ~22 % of species shared with the Proto-Mediterranean Sea. The faunistic similarity decreased successively at higher latitudes towards the northeastern Atlantic and dropped to low values towards the North Sea. Therefore, a connection with the North Sea can be excluded throughout the Early and Middle Miocene. Faunistic relations of the Central Paratethys Sea with the Eastern Paratethys Sea were surprisingly low until the late Middle Miocene, when endemic species from the Eastern Paratethys ‘flooded’ the Central Paratethys. Therefore, the effectiveness in species transfer or presence of the Carasu and Barlad straits, hypothetically connecting both seas, must be questioned for most of the Middle Miocene.The present-day gastropod faunas of the tropical eastern Atlantic (TEA) and the Indo-West Pacific Region (IWP) can be distinguished clearly by their differing faunal structure (different relative abundance of certain families). The faunas of the Paratethyan and the Proto-Mediterranean Sea follow more closely the type nowadays represented in the tropical eastern Atlantic, suggesting a common origin. The faunistic connectivity with the Indian Ocean, via the Tethys Seaway ceased very early during the Early Miocene, predating the formation of the Gomphotherium land bridge by several million years. Consequently, we reject a re-activation of the Tethys Seaway during the Langhian as providing an effective oceanographic gateway. This is an important observation for climate models, linking the closure of the Tethys Seaway to Miocene climate change.

Preliminary Data on the Species Composition and Distribution of Land Snail (Mollusca: Gastropoda) in Son Doong Cave, Phongnha - Kebang National Park

Son Doong Cave it is the largest cave on the planet and also the most majestic cave in Vietnam. Son Doong Cave is divided into habitats: Dark cave (covered by the cave ceiling) and light cave (not covered by the cave ceiling), including doline 1 and doline 2.Surveying and collecting land snail samples in Son Doong cave was carried out in January 2023. For the first time, the list of terrestrial snail species in Son Doong Cave was published. This includes 30 species (11 phenotyps are just only identified to genus) belonging to 24 genera, 11 families, 3 orders, 3 subclasses; of which the presence of 5 species (Pincerna mouhoti, Leptopoma perlucidum, Scabrina patera, Chloritis khammouanensis, Amphidromus haematostoma) are newly recorded and added to the list of terrestrial gastropod fauna of Vietnam. In Son Doong cave, land snails are only distributed in the light part of the cave (Doline 1 and Doline 2), not in the dark part of the cave, which accounts for most of the cave area. Doline 2 has a higher species diversity (27 species belonging to 22 genera, 8 families, 2 orders) than Doline 1 (13 species belonging to 11 genera, 6 families, 3 orders). The diversity of land snail species in Son Doong cave is very unique and highly distinctive, but the species populations here is very small, requiring recommendations for tourists and the management board to protect vegetation to maintain and develop populations of this species.

Pleurotomariida (Gastropoda) from the upper Anisian platform carbonates of the Dolomites (Southern Alps, Italy): systematics, palaeobiogeography and Triassic recovery

AbstractA very rich gastropod fauna from the upper Anisian (Nevadites secedensis Zone) platform carbonates of the Dolomites, represented by more than 200 species, was collected over recent decades. Its study contributes to a better understanding of the dynamics of the recovery after the end‐Permian mass extinction. This paper deals with the Pleurotomariida. A total of 35 species, 22 genera and 9 families have been identified. Of these, 12 species and 7 genera are new, namely Rufilla wilckensi sp. nov., Rufilla giacomellii sp. nov., Viezzenella ruvida gen. et sp. nov., Temnotropis maestroettorei sp. nov., Cancellotomaria boninsegnai sp. nov., Stuorella crenulata sp. nov., Codinella? fontanai sp. nov., Fiacconella pericincta gen. et sp. nov., Fiemmespira gen. nov., Texturaspira gen. nov., Nodocingulum ogilvieae sp. nov., Dimorphotomaria fassaensis gen. et sp. nov., Moenaspira crassa gen. et sp. nov. and Predazzella elongata gen. et sp. nov. Comparison with the gastropod fauna of the St Cassian Formation indicates that, from the late Anisian to the Carnian, in the Dolomites the richness of the Pleurotomariida increased by 54% at species level, 26% at genus level and 22% at family level. A comprehensive palaeobiogeographical analysis highlights a very high degree of endemism: 90% of the species are exclusive to single palaeogeographical units. This suggests that species diversification at a strict local scale was a major feature of the Middle Triassic phase of recovery of the Pleurotomariida. Seemingly, the non‐planktotrophic development of this group combined with a patchy resurgence of the carbonate platforms played an important role in hampering dispersal.

Middle Miocene (Late Badenian) microvertebrates from Hidas, SW Hungary

Up to the present, no terrestrial vertebrate fauna has been published from the pre-Pannonian Miocene of SW Hungary. In 2022 a microvertebrate assemblage was unearthed from a lime mud bed of the Middle Miocene Hidas Formation, in an abandoned coal mining field close to Hidas in the Mecsek Mts. The herpetofauna and the rodent material are described here. Fossil findings point to the Late Badenian MN 7+8 Zone, which, together with the earlier results based on the marine mollusc fauna, narrows the age of the unit to ~13.5–13.3 Ma. The amphibians and reptiles are aquatic, semiaquatic or periaquatic forms. Sedimentary features and the accompanying freshwater gastropod fauna are indicative of a shallow pond or a paludal depositional environment. Crocodylian finds reported earlier from the Hidas Formation indicate a subtropical climate, just before the end of the Miocene warm period in Central Europe. Among the rodents, glirids and flying squirrels as well as Democricetodon and Megacricetodon indicate the presence of humid arboreal vegetation around the site. The rodent taxa are well known from the Middle Miocene faunas of northern Hungary, western Romania and from the Upper Freshwater Molasse of southern Germany and Switzerland. The rodent material does not show characteristics of an insular fauna, e.g. gigantism or endemism. Consequently, although the coeval palaeogeography of the region has been described as an archipelago in the Central Paratethys, with the Mecsek Mts. being one of the islands, the area must have had ecological connections towards the northern and eastern parts of the Pannonian Basin, and the marine areas within the archipelago did not form a barrier against the distribution of microvertebrates. The corridor could have been located towards the NE from the Mecsek Mts., across the elevated basement blocks of central Hungary.

Litter-dwelling terrestrial molluscs of Nepisiguit Protected Natural Area and Mount Carleton Provincial Park, north-central New Brunswick

No comprehensive study of the terrestrial gastropod fauna of northern New Brunswick has previously been undertaken. Most terrestrial gastropod molluscs are tiny and generally live unnoticed under debris, in leaf litter, and among other dead and living vegetation. Sifting and sorting collected samples of leaf litter are effective in sampling snails. In June–July 2015 and August 2016, 43 samples of forest leaf litter were collected in Nepisiguit Protected Natural Area and Mount Carleton Provincial Park. These samples yielded 22 species of terrestrial gastropods. Seven species are reported from New Brunswick for the first time.

The gastropod fauna from Intertidal zone of Siridao beach, Goa, India

The gastropod fauna from Intertidal zone of Siridao beach, Goa, India

Laetoli, Tanzania: Extant terrestrial mollusc faunas shed new light on climate and palaeoecology at a Pliocene hominin site.

Laetoli, Tanzania is one of the most important palaeontological and palaeoanthropological localities in Africa. We report on a survey of the extant terrestrial gastropod faunas of the Laetoli-Endulen area, examine their ecological associations and re-examine the utility of Pliocene fossil molluscs in palaeoenvironmental reconstruction. Standardised collecting at 15 sites yielded 7302 individuals representing 58 mollusc species. Significant dissimilarities were found among the faunas of three broad habitat types: forest, woodland/bushland and open (grassland and scattered, xeric shrubland). Overall, more species were recorded in the woodland/bushland sites than in the forest sites. Open sites were less diverse. Environmental factors contributing most strongly to the separation of habitat types were aridity index and elevation. The results are supplemented with new mollusc data from the Mbulu Plateau south of Lake Eyasi, and compared to the list of species cumulatively recorded from the Ngorongoro area. Some regional variation is apparent and historical factors may explain the absence of some fossil taxa from Laetoli today. Differences in seasonality separated upland forest sites on the Mbulu plateau from those at Lemagurut at Laetoli. Indicator species were identified for each habitat. These included several large-bodied species analogous to the Laetoli Pliocene fossil species that were then used for palaeoenvironmental reconstruction. Based on the estimated aridity index, and adopting the widely used United Nations Environment Programme (UNEP) global climate classification, the four stratigraphic subunits of the Upper Laetolil Beds (3.6-3.85 Ma) would be placed in either the UNEP's Dry Sub-humid or Semi-arid climate classes, whereas the Upper Ndolanya Beds (2.66 Ma) and Lower Laetolil Beds (3.85-<4.36 Ma) would be assigned to the Humid and Semi-arid climate classes respectively. Pliocene precipitation at Laetoli is estimated as 847-965 mm per year, refining previous estimates. This is close or slightly higher than the present mean annual precipitation, and is likely to have corresponded to a mosaic of forest, woodland and bushland within a grassland matrix consistent with other reconstructions.

The Early Pleistocene freshwater mollusks of the Denizli Basin (Turkey): a new long-lived lake fauna at the crossroads of Pontocaspian and Aegean-Anatolian realms

We describe here a newly discovered, diverse fossil fauna of freshwater gastropods and bivalves from the Denizli Basin in SW Turkey. The material was collected from the Kolankaya Formation, for which latest chronostratigraphic and magnetostratigraphic data indicate an Early Pleistocene age, which is much younger than previously assumed for the fossil-bearing strata of the Denizli Basin. The fauna consists of at least 27 species (25 gastropods, 2 bivalves) and includes a new genus,Harzhauseriagen. nov., and 6 new species within the Hydrobiidae: Falsipyrgula ? coronatasp. nov., Graecoanatolica ? alcicekorumsp. nov.,Harzhauseria schizopleuragen. et sp. nov.,Iraklimelania minutissimasp. nov.,Iraklimelania submediocarinatasp. nov., and Xestopyrguloides ? sagittasp. nov.Additionally, we define lectotypes forStaja orientalis(Bukowski, 1896) andValvata orientalisFischer, 1866, as well as a neotype forTheodoxus percarinatus(Oppenheim, 1919). Nine of the recovered species (33.3%) are only known from the Denizli Basin. Almost half of the fauna (44.7%) is endemic to the Aegean–Anatolian region, with biogeographical affinities to the Pliocene–Early Pleistocene faunas of Rhodes, Kos, and mainland Greece, as well as the Çameli and Eşen Basin in Turkey. On the genus level, the fauna also contains several typical Pontocaspian elements. The composition points toward a typical long-lived lake environment with oligohaline conditions.

Radix rufescens (J. E. Gray, 1822) (Gastropoda: Lymnaeidae), a new species for Oman and Arabian Peninsula

The fauna of freshwater gastropods of the Arabian Peninsula, a desert land, is neither rich nor extensively studied. Only five species of the family Lymnaeidae have been recorded from this subcontinent so far. In February 2023, a few specimens of Radix rufescens (J. E. Gray, 1822) have been collected from the stream at Wadi Tiwi, NE Oman. The shell, female part of the reproductive organs, prostate, paraeputium and phalloteca are presented. Cytochrome oxidase subunit I (COI) sequences confirmed the assignment of these specimens to R. rufescens, known from Nepal, Bangladesh, and Myanmar, not from the Arabian Peninsula. Either R. rufescens is the sixth lymnaeid species inhabiting Arabia, or at least some of the records of R. natalensis (Krauss, 1848), whose shells are hardly discernible from the ones of R. rufescens, should be interpreted as misidentified R. rufescens. Thousands of years of the trade relations between Oman and India suggest accidental transportation of this snail by trade vessels.

Freshwater gastropods across the Cretaceous–Paleogene boundary in the Songliao Basin, north-east China

Gastropod faunas from the Cretaceous–Paleogene (K/Pg) boundary transition in the well-dated Songliao Basin (north-east China, East Asia) have been studied. In total, 673 specimens were counted, of which about 80% (n = 538) could be identified. In all, eight species, belonging to six genera, have been identified, including Hydrobia? datangensis, Mesolanistes cf. nanxiongensis, Valvata jiaolaiensis, Valvata shakengensis, Tricula sp. 1, Tricula sp. 2, Zaptychius sp., Planorbidae gen. et sp. indet. and Helisoma dongdawusuensis. Combining data on species ranges in the Jiaolai and Pingyi basins of eastern China, it is shown that three out of 11 species went extinct during K/Pg boundary perturbations. Therefore, we conclude that freshwater gastropods in East Asia underwent minor extinction (c. 18% extinction rates; 72% survival rates). These snail faunas were not affected by short-lived detrimental conditions related to K/Pg boundary perturbations, such as darkness, cooling and starvation, because most of these genera are micro-herbivorous and/or micro-omnivorous grazers (including detritivores) that fed on bacterial films, algae and diatoms or ingested carrion and fine organic deposits. The global mass extinction event at the K/Pg boundary in freshwater environments has rarely been studied, meaning that the present study may help to understand patterns of selective extinction.

The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications.

In this work, all the Lower Pliocene gastropod assemblages of Santa Maria Island are revised. These all form part of the Touril Complex. Seventy-seven species are identified representing 61 genera. Two species are described as new: Bittium miradouroense nov. sp. and Erato mayeri nov. sp. The name Tritonium secans Bronn in Reiss 1862 is considered a junior subjective synonym of Monoplex comptus (A. Adams, 1855). Pleurotoma perturrita Bronn in Reiss 1862 is considered a junior subjective synonym of Crassopleura maravignae (Bivona, 1838). However, due to the difficulties in collecting from these deposits, this is likely to be a considerable underestimate of the original diversity of local Early Pliocene gastropod faunas. The assemblage reflects a fully tropical with mean annual sea surface temperatures (SSTs) estimated about 3.7°C to 6.3°C higher than the present-day 20.6°C, and with mean monthly SSTs ranging from 20°C to 28°C, with six months with mean SSTs over 24°C. The assemblages all represent relatively shallow water, fully saline marine environments. At genus level the assemblage is typical of that seen in the tropical Mediterranean-West African Palaeobiogeographical Province during the early Pliocene (MPPMU1; roughly equivalent to the Zanclean and earliest Piacenzian). At species level, 35% of the species taxa found in Santa Maria are also found in the Mediterranean during MPPMU1. There is a much weaker association with the northern warm temperate Pliocene Boreal-Celtic Province, with only 17% of species occurring in both. Moreover, most of those are ubiquitous European species with both wide geographic and stratigraphic distributions. The assemblage is relatively endemic (29%) suggesting that the Azorean subprovince/ecoregion, which is recognised today, was already in place in the Lower Pliocene. A small number of tonnoidean species found in Santa Maria are species known to have had an amphiatlantic distribution during the Pliocene, and for Distorsio mcgintyi Emerson & Puffer, 1953, a well-known and widely distributed tropical American Atlantic species from the Early Miocene to present-day, its presence in Santa Maria marks the most easterly range expansion for the species, as today is not found in the Azores.

Biodiversity of extant snails (Gastropoda, Mollusca) in the Pliocene Mountain Spur Natural Reserve (Northern Apennine, Italy).

To date, there is a substantial lack of information about gastropods from the Tuscan-Emilian Apennine in the north of Italy, notwithstanding the availability of detailed and comprehensive literature on this molluscan class. We present a gastropod fauna from the Natural Reserve of the Pliocene Mountain Spur: to our knowledge, this is the first investigation of the extant gastropod fauna in the Tuscan-Emilian Apennine and one of the few in the Apennine's mountain chain as a whole. We describe a gastropod fauna comprised by 25 species, belonging to 18 genera and 10 families: the general figure which is emerging is an assemblage of European and Mediterranean-European species, with a single Asian contribution. Several shells were collected as embedded in sandy-clayey soils and showed fossilisation traces: therefore, we regard these shells as subfossil samples. Namely, subfossil shells are from the species Pomatiaselegans, Granariafrumentum, Retinellaolivetorum, Xerolentaobviaobvia, Oxychiluscf.draparnaudi, Monachacartusiana and Monachacantiana. The present checklist is the first report in the Tuscan-Emilian Apennine and Emilia-Romagna areas for six taxa: Morlinaglabraglabra, Oxychiliusalliarius, Xerosectacespitum, Fruticicolafruticum, Xerogyraspadae and Xerolentaobviaobvia.

Diversity and genetic connectivity of heteropod (Pterotracheoidea) gastropods in the Tropical Eastern Pacific

AbstractPrevious research focusing on pelagic gastropods in the open ocean has demonstrated that many morphospecies comprise multiple distinct clades or cryptic species that can be distinguished with DNA sequence data. To date, the genetic diversity of the pelagic gastropod fauna of the tropical East Pacific, especially in shallow coastal waters, remains largely unexplored. To document the diversity of pterotracheoids (formerly heteropods) from the coastal waters of the Bay of Panama, we collected, photographed and sequenced fragments of mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal DNA for 60 atlantids, 3 carinariids and 6 pterotracheids. In addition to the COI barcode, our results include the first published 16S sequences for these groups. We found 11 operational taxonomic units (OTUs): 9 in the genus Atlanta, 1 Carinaria and 1 Firoloida. We report the presence of Atlanta oligogyra (Clades A and B), Atlanta turriculata, Atlanta lesueurii, Atlanta helicinoidea (Clade B), Atlanta plana, Atlanta echinogyra, Atlanta inflata and Atlanta frontieri through comparisons of our sequences with previously published sequences. We did not find Atlanta gaudichaudi, Atlanta inclinata, Atlanta tokiokai, Atlanta gibbosa, Atlanta peronii, or Oxygyrus inflatus, which have previously been reported from the region. Haplotype networks and estimates of ΦST illustrate how some species show population differentiation across the tropical Indo‐Pacific region, whereas others show little apparent population structure. For example, the most common haplotypes of A. inflata and of A. turriculata occur in the Indian Ocean, the Central and West Pacific and the tropical East Pacific, whereas individuals of A. frontieri from the Indian Ocean do not share haplotypes with individuals of A. frontieri from the Pacific Ocean. Analyses were limited by sample sizes, but these data suggest that population genetics approaches may be useful for reconstructing population histories of these important, but overlooked, components of the plankton.

Micropaleontological findings and absolute ages mark the termination of the Last Glacial Maximum in the Eastern Mediterranean Region: New electron spin resonance data from Gediz Delta (Western Turkey)

Sediments and fossil content of Gediz Delta (Eastern Aegean Sea-İzmir) were examined from the samples collected from three drilling cores from the west (seaward) to east (landward) of the delta. Each drilling core contains Quarternary marine deposits with a marine fauna of foraminifers, bivalves, gastropods, echinoids, and ostracods at the bottom and Quaternary continental delta deposits at the top. According to our Electron Spin Resonance (ESR) age model marine sediments of the Aegean Sea started to cover the western Gediz Delta area before 19.9 ka (thousand years). Following the Last Glacial Maximum (LGM), after the transgression due to deglaciation occurred 15.3 ka ago, the coastline progressed 15-20 km eastward and covered the entire delta area. At the end of the LGM, as a result of the overflow of Manisa Gediz Lake depending on the deglaciation in Western Anatolia, and its flow from the Emiralem Strait to the İzmir Bay, the continental deposits reaching the West Gediz Delta region are younger than 11.4 ka.

Ilona Valley revisited – A rich early Miocene gastropod fauna from the North Hungarian Basin

A new mollusc material from the Ilona Valley Section (Mátra Mts, Hungary) is investigated. Strata of the section represent the Ilonavölgy Member of the Pétervására Sandstone Formation. Based on geochemical data and mollusc biostratigraphy these deposits appear to be early Ottnangian in age. Th e mollusc fauna displays much higher diversity than was recognized in earlier studies from the locality in question and from other Ottnangian sites in the Paratethys. Th e rich material verifi es the extended stratigraphic and palaeogeographic ranges of numerous taxa, and allows of designating 12 new gastropod species: Clanculus s. l. gulyasi n. sp., Gibbula kralli n. sp., Calliostoma nandori n. sp., Ormastralium erazmusi n. sp., Sconsia landaui n. sp., Cirsotrema kokayi n. sp., Ocinebrina deaki n. sp., Calagrassor mathiasi n. sp., Clavatula s. l. barnabasi n. sp., Clavatula s. l. istvani n. sp., Dentimargo barnai n. sp., Solatisonax pozsgayae n. sp. With 106 fi gures and 1 table.

Synopsis of gastropod-associated nematodes of Ciscaucasia (Russian Federation) with the description of a new species of Pellioditis Dougherty, 1953 (syn. Phasmarhabditis Andrássy, 1976).

Caucasus is known as one of the few biodiversity hotspots in Europe and is characterised by rich gastropod fauna while the nematode fauna in association with gastropods has remained largely understudied. Surveys conducted in 2019 and 2021 in the North Caucasus of the Russian Federation (Stavropol Upland and western and central parts of Krasnodar Krai) has revealed the presence of three new species of Pellioditis, a facultative parasite of land gastropods, and two species of obligate parasites, the intestinal parasite Angiostoma kimmeriense and a new, still undescribed species of a larval ectoparasite Alloionema sp. The new associations of Cruznema sp. and Rhabditophanes sp. with land gastropods were recorded for the first time in the Russian Federation. The new species of Pellioditis Dougherty, 1953 described here is based on the analysis of morphology and molecular studies of two distant and morphologically distinct strains, thermalis and sindicae. Pellioditis thermalis n. sp. was characterised by females possessing a tail of about 95-100 μm long, broadly conical in shape in the thermalis and sindicae strains, with a rounded anterior part and a subulate terminal part as long as the former; prominent phasmids located at the mid-tail, equatorial vulva position, a lateral field of three ridges (four incisions), males with spicules featuring a hole at the distal tip, ensheathed infective juveniles with average length 717 μm in the thermals strain and 771 μm in the sindicae strain, and exsheathed ones 644 μm and 682 μm, respectively. ITS-based phylogenetic analyses revealed that all Pellioditis species found in Ciscaucasia and Transcaucasia probably belong to two separate clades, with independent evolutionary histories of colonisation of this area. The entire Caucasus range area appears to serve as a biodiversity hotspot for the genus Pellioditis, presumably due to its complicated geological history and repeated isolation events for its terrestrial mollusc hosts.

HABITAT USE AND SPECIES RICHNESS OF MARINE MOLLUSCS ALONG THE TUTICORIN COAST, GULF OF MANNAR, INDIA

Molluscs are considered the largest marine phylum, comprising about 23% of all marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. Gastropods and bivalves were collected from different stations in the coastal area of the Gulf of Mannar on the Tuticorin Coast, Tamil Nadu, India. In the present investigation, 30 species of gastropod fauna and 13 species of bivalve fauna were recorded from January 2021 to June 2021. During the study period, the bivalves Babylonia spirata and Pinctada fucata were abundant among the gastropods. The maximum density of gastropod and bivalve fauna was recorded at Therespuram. This research is an attempt to gain a better understanding of the possibility of ecological value and ecosystem conservation of molluscan fauna.