Molluscs of the genus Corbicula, first discovered in the lower Don River (Novocherkasskaya TPP warm channel area) in 2017, were identified as Corbicula fluminea based on their conchological features.  The aim of the present work was to obtain new data on morphometry and peculiarities of shell-shape forming of molluscs of this species from the Don River in ontogenesis. Using the main morphometric parameters of the shell – length (L), width (D) and height (H) – changes in its frontal (D/L), sagittal (H/L) curvature (=Index of Roundness), convexity ((H+D)/L) and conditional volume (H×D×L/1000) indices during ontogeny were shown. The relevant equations of dependencies are given. The conclusion was made about the interval type of changes in the indicated curvature indices, which determine the corresponding changes in the relative volume of the shells in ontogenesis.. Their graphs have a dome-shaped character with reaching values in the range of shell lengths 15–25 mm, reliably exceeding similar values in the intervals up to 15 and more than 25 mm. Sexual maturation and the onset of reproduction of molluscs occurs at the stage of increasing relative shell volume. This strategy of shell formation, aimed at creating the maximum internal relative volume of the shell during the period of gonad formation, especially in the androgenic C. fluminea, which incubates larvae, may be one of the characteristics that determine the reproductive capacity of the species and, consequently, its invasiveness.

A revision of Black Sea chitons of the genus Lepidochitona has been conducted. The revision revealed new features of intrageneric similarity and differences of Black Sea species as well as with Mediterranean species. Species similarity of Black Sea and Mediterranean representatives of Lepidochitona cinerea is confirmed. A new species L. bondarevi sp. nov. is described. Previously its specimens were attributed erroneously to L. caprearum. The new species differs from L. caprearum in having a less broad head valve, shorter apophyses, a much longer postmucronal area on the tail valve, 7–8 longitudinal grooves around the upper half of dorsal girdle spicules and smooth dorsal girdle needles.

The aquatic gastropod Lymnaea stagnalis exhibits a high variability of conchological features. To assess the degree of variation in the size and shape of the shell in the populations of this species inhabiting the Central Russian Upland, a comparative analysis was carried out using the methods of classical and geometric morphometry. A pairwise comparison of populations using the Post-hoc test for perMANOVA has shown that when using geometric morphometry, there were more statistically significant differences between the groups of snails compared than when using classical conchiometric analysis. In addition, the pattern of distribution of populations by groups during clusterization differed significantly when using different morphometric methods. We believe that the methods of geometric morphometry, which make it possible to give an integral characteristic of the shell, are better suited for understanding the patterns of microevolutionary processes in populations of gastropods, as well as studying the ecological characteristics of species. Nevertheless, in order to prevent the loss of important conchiometric data that can be used for species identification and assessment of intra- and inter-population variability, when using geometric morphometry, it is also important to take into account the absolute dimensional characteristics of the object of study.