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.