A new genus of stygobiont hydrobiid snails, endemic to Georgia, is described. Sitnikovia gen. nov. includes two species: S. megruli sp. nov. and S. ratschuli sp. nov., known only from their type localities (Garakha and Sakishore caves). The data of shell characters, penial morphology, and radula of the new genus are provided.
A taxonomic revision of the stygobiont microsnails from north-western Transcaucasia (Krasnodar Krai, Russia) is presented. Two new genera—Schapsugia gen. n. and Tachira gen. n. are established. It is shown that the genus Paladilhiopsis does not occur in this area, and the snails previously assigned to this genus belong to Schapsugia gen. n. Two nominal species Paladilhiopsis orientalis Starobogatov, 1962, and P. subovata Starobogatov, 1962 are considered junior synonyms of Sch. pulcherrima (Starobogatov, 1962), based on a re-examination of their conchological variation. In addition, two more species of Schapsugia are described: Sch. kudepsta sp. nov. and Sch. occultata sp. nov. The anatomical structure of another species, Geyeria valvataeformis Starobogatov, 1962 was studied for the first time. It is revealed that it should be placed in a separate genus (Tachira gen. n.). Thus, the previously proposed placement of the microsnails from north-western Transcaucasia in hydrobiid genera from the Balkan Peninsula (Geyeria, Paladilhiopsis) is rejected.
The species of the Ponto-Caspian gastropod genus Clathrocaspia Lindholm, 1930 have been recorded so far from the Caspian Sea Basin only from marine waters, whereas they inhabit the estuarine areas as well as the purely freshwater environments in the Azov–Black Sea Basin. This genus has recently been assessed as putatively extinct in the Caspian Sea. A new purely freshwater species Clathrocaspia laevigata sp. n. from the water-flows of the Samur River delta in Dagestan, Russia, is described. A morphological comparison of the new species with C. brotzkajae (Starobogatov in Anistratenko & Prisjazhnjuk, 1992) from the Caspian Sea and C. knipowitschii (Makarov, 1938) inhabiting the Azov–Black Sea Basin shows their overall similarity. The major difference is that C. laevigata sp. n. almost completely lacks the reticulate teleoconch sculpture, whereas it is well-developed in all known Clathrocaspia species. The molecular data revealed probable sister relationships between the new species and C. knipowitschii. All Dagestan populations are ecologically and spatially isolated from the open sea and and are very locally restricted. We suggest to consider newly described snail species as retained in a pure freshwater refuge located in the coastal area of the Caspian Sea. The discovery of such a refuge sheds more light on the origin, current state and the future of the unique Ponto-Caspian aquatic biota under global change and increasing anthropogenic impact.
Since 2020, the south-western Caucasus has been recognized as a hotspot of stygobiotic Mollusca diversity after revealing a large number of new, range-restricted species within the spring snail family Hydrobiidae, subfamily Sadlerianinae sensu Szarowska. Meantime, based on extensive material collected in the south-western Caucasus during the last decades, we studied members of another spring snail subfamily Belgrandiellinae Radoman, 1983. Modern integrative taxonomic work revealed hitherto unknown diversity within this subfamily in the region and further proved the importance of the south-western Caucasus as a hotspot of stygobiotic life. In particular, the subterranean environment and springs of Georgia were known to be inhabited by the genus Tschernomorica Vinarski and Palatov, 2019 with four nominal species. Our research, based on a morpho-anatomical study and genetic investigation of COI/H3 mitochondrial/nuclear markers, revealed additionally seven species and three genera new to science—Colchiella lugella gen. et sp. nov., C. nazodelavo gen. et sp. nov., C. shiksa gen. et sp. nov., C. dadiani gen. et sp. nov., Sataplia cavernicola gen. et sp. nov., Aetis starobogatovi gen. et sp. nov., and Tschernomorica kopidophora sp. nov. —to inhabit the Georgian part of south-western Caucasus. The full taxonomic description of each new taxa, along with the review of habitat characteristics and conservation status, is provided. Molecular genetics suggests that the ancestors of Caucasian Belgrandiellinae have migrated from south-western Europe, probably more than once during the late Messinian and early Pliocene periods. Later, Plio-Pleistocene climate oscillations, particularly the repeated rise and fall of the Black Sea water level, resulted in the isolation and radiation of various lineages within the Caucasus and Crimea.
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