Volume 36

The new species, Vallonia yakutica sp. nov. is described from the central part of the Republic of Sakha (Yakutia). The population lives on the edge of the forest of larch (Lárix sibírica ldb.), and birch (Betula pendula Roth.) trees, with various herbs. The presence of herbs is necessary for the habitat of Vallonia yakutica sp. nov. which feeds on their fallen leaves. The maturity of the snail is achieved in two years. The differences between the new species from the morphologically most close Vallonia kamtschatica Likharev, 1963 are discussed.

The response of mollusk communities to radioactive contamination in natural freshwater ecosystems remains understudied. We have analyzed the data on species composition of bivalve and gastropod mollusks inhabiting the «Mayak» Production Association (PA) (Russia, Chelyabinsk Region) special industrial reservoirs (R-3, R-4, R-10, R-11, R-17). These waterbodies have the status of facilities of atomic energy industry (the “atomic heritage”) and are used as storages of liquid radioactive waste. The Shershnevskoye Reservoir (Chelyabinsk City, Russia), a waterbody with background activity concentration of anthropogenic radionuclides, has been studied as a control site. Radioactive contamination has led to chronic exposure of freshwater mollusks. The dose rate ranges were as follows: 6–14 mGy/day for reservoir R-11; 16–40 mGy/day for reservoir R-10; 37–73 mGy/day for reservoir R-4; 49–72 mGy/day for reservoir R-3; 1,270–2,370 mGy/day for reservoir R-17. It has been found that chronic radiation exposure leads to a decrease of mollusk species diversity. 21 species of bivalves and 35 species of gastropods were registered in the control waterbody. In radioactively contaminated sites, a sharp decrease in species diversity has been observed. For example, in reservoir R-11, 7-fold decrease in the number of bivalve mollusk species and 2-fold decrease in the number of gastropod species as compared with the control reservoir have been recorded. In R-10 and R-4, the number of bivalve species was reduced 20-fold and the number of gastropod species was reduced 5- and 9-fold, respectively. In R-3, no bivalves were registered, and the number of gastropod species was reduced 6-fold. No mollusks were detected in R-17. Among all hydrobionts, pelophilous bivalves of the family Sphaeriidae, as well as gill-breathing snails (Gastropoda, Caenogastropoda), whose life cycle is associated with bottom sediments, are the most vulnerable to the effect of chronic radiation exposure.

Age-related variability of the shell valves and radula in two species of the genus Callistochiton and one species of the genus Ischnochiton is discussed based on the photographs obtained with a scanning electron microscope. Particular attention is given to the shape and sculpture of the valves, as well as the shape and number of teeth in the transverse row of the radula. It is shown that even such a key feature of the genus Callistochiton as radial ribs on the head, intermediate and tail valves is absent at the early stages of development and appears only when the body length reaches 4–5 mm. The results of studying age-related variability are of great importance for the taxonomy of both recent and fossil mollusks.

A description of Turanena gissarika sp. nov. from the Gissar Ringe is presented. Conchologically, the new species is most similar to T. cognata, but anatomically it differs in having a tubercle-like swelling on the opposite side of the caecum.

The morphological features and ultrastructure of the hinge margin of the giant oyster Magallana gigas larvae, which were obtained from a nursery with the Black Sea broodstock and grown under optimal conditions, were studied. The paper presents scanning electron micrographs of disarticulated larval valves at different stages of development. In larvae at the D-veliger stage (2 days old, shell dimensions: 72×62 μm), as well as at the veliger stage (shell dimensions: 84×96 μm), the provinculum of the right and left valves consists of two anterior and two posterior teeth. We noted 2 to 3 teeth on the provinculum in both ”uneyed“ (H: 140–182 μm) and ”eyed“ velikonch larvae (H: 200–230 μm) on the anterior and posterior edges of the right and left valves. In pediveligers (H: 338–358 μm) there are two anterior teeth in the hinge margin of the right and left valves; the posterior teeth are reduced. We also determined logarithmic dependences of the hinge margin length (l, μm) on the length (L, μm) of the shell [l=32.518•ln(L) – 96.35; R2=0.904] and the maximum provinculum width on the shell height [c=5.8937•ln(H) – 17.994; R2=0.8993] of larvae ranging in size from 72×62 to 322×358 μm. The morphological characteristics and provinculum ultrastructure of the reared larvae were compared with those of M. gigas larvae of Atlantic and Pacific origin. The article discusses the potential hybrid nature of the Black Sea broodstock.

The taxonomic status of Indoartemon vietnamensis Thach, 2020 is reassessed. The morphology of I. vietnamensis falls within the intraspecific variation of I. huberi (Thach, 2016). The similarities suggest that I. vietnamensis should be treated as a junior subjective synonym of I. huberi. Furthermore, a new subspecies of the genus Indoartemon is described from Chua Chan Mountain, Dong Nai Province, Vietnam. Indoartemon huberi chuachanensis subsp. nov., has oblique-heliciform shell with axially deflected last whorl, narrow and deep umbilicus, aperture with one strong parietal lamella and one small palatal lamella, slightly enlarged columellar fold along the columellar margin.

Gastropod mollusk Jujubinus exasperatus is recorded for the first time in the Black Sea off the coast of Crimea. A brief species diagnosis, photographs of the shells and live specimen in situ are provided. Previously, the species was listed for the fauna of Russia and the Black Sea based on literary sources, the reliability of the information discussed in this paper. The possibility of naturalization of J. exasperatus in the Black Sea ecosystem is considered. J. exasperatus is recognized as an accidental element of the Black Sea benthos.

Three new species have been added to the formerly monotypic genus Liobaicalia Martens, 1876. We employed a combination of morphological, anatomical, and molecular approaches using mitochondrial COI gene, nuclear ATP-synthase alpha subunit gene intron (ATPase), and ITS1 spacer to delineate species boundaries between Liobaicalia stiedae (W. Dybowski, 1875), L. sidelevae sp. nov., L. karabanovi sp. nov., and L. riedeli sp. nov. The Liobaicalia species inhabit burrowing into sandy substrates in disparate regions of the ancient and/or recent deltas of the inflows to the south and central Baikal basins near tectonic faults where gases discharge happens. The genus Liobaicalia was not recovered as monophyletic based on current molecular-phylogenetic analyses based on mitochondrial COI data. We discussed discordance between morpho-anatomical and genetic traits, the possible origin of the Liobaicalia species, and the occurrence of scalariform shells in Baikal and non-Baikal gastropods belonging to different families.

The generic name Cryptobranchia Middendorff, 1851 is a junior objective synonym of Lepeta J.E. Gray, 1842. Designation of Patella caeca var. concentrica Middendorff, 1848 as a type of Cryptobranchia is invalid. For two species previously assigned to the genus Cryptobranchia [Lepeta concentrica (Middendorff, 1848) and Acmaea kuragiensis Yokoyama, 1920], the new generic name Cryptolepeta gen. nov. is proposed.