The development of the larval shell and hinge of the bivalve mollusk Macoma balthica in the White Sea is described. Macoma spawning occurs at the end of June. Larvae at the D-stage of development have a shell length of 120-140 µm. The shell is oval, the hinge edge is straight with a noticeable striation. During development, the shell becomes more elongated with a pointed anterior end. A characteristic feature is the expressed concentric striation of prodissoconch II. The umbos are low and rounded. Hinge edge is straight, with small teeth of provinculum. The ligament occupies the central position. At later stages, a pair of large hook-shaped teeth is formed in the anterior part of the hinge. Metamorphosis occurs at shell length of 300-310 µm.

A new genus Barbadoschiton gen. nov. [type species B. bromleyi (Ferreira, 1985)] of the family Ischnochitonidae from shelf near Barbados and Martinique Islands is described. The genus possesses unique features of the tegmentum and girdle. The central area of the intermediate valves and antemucronal area of the tail valve show teardrop-shaped granules arranged in quincunx and have only one pore of aesthete. The marginal fringe of girdle is beset with five kinds of elements, among these long, fine needles, flattened, obtuse pointed spicules with three ribs on one side; spicules with longitudinal groove on one side and with 7 longitudinal ribs, on the other side; numerous, small spicules with 5 longitudinal ribs and one longitudinal groove; flat, obtuse spicules with two warts on upper half. The ventral spicules are of two kinds: main flattened, rectangular spicules with distal appendix and three weak longitudinal ribs on external part; and small distally pointed, smooth on the outer side and with two longitudinal grooves on the opposite side of the spicules. The latter are attached in transverse rows with their proximal part between the main ventral spicules. The major lateral teeth of the radula have a tridentate head, with the middle denticle being longer than others.

The available data about the recent distribution of slugs of the family Arionidae on the territory of Belarus are summarised. The findings of a species formally new to the malacofauna of Belarus, A. fasciatus, are discussed. The material was collected in the period from 2018 to 2024 on the territory of the Gomel region (South-Eastern Belarus). The original illustrations of the habitus and anatomical features of the reproductive system are given.

The genus Caspiohydrobia belongs to the less-known taxa of the family Hydrobiidae. According to a conchologically-based system, developed in the 1970-1980s by Yaroslav I. Starobogatov and his co-authors, the genus includes around 30 living species. However, the most recent data based on molecular evidence indicate that most (if not all) of these morpho-species should be considered junior synonyms of a widely distributed species, Ecrobia grimmi. However, the vast majority of nominal species described in the genus Caspiohydrobia have never been reassessed by molecular taxonomic methods. In this work, the genetic diversity of Caspiohydrobia spp. was studied based on a large sample taken in Lake Elanach in the Kurgan region (Trans-Urals, Russia). Conchological analysis made it possible to identify 7 nominal species of the genus Caspiohydrobia in the sample, whereas genetically all the studied individuals were the same, sharing a single COI haplotype. A phylogenetic tree of Ecrobia spp. has shown that all studied genetically specimens of Caspiohydrobia (including newly sequenced ones) forms a separate cluster on a cladogram, which can be identified as Ecrobia grimmi s. lato. However, a higher genetic diversity was revealed in a population of Caspiohydrobia spp., from a lake adjacent to the Caspian Sea (West Kazakhstan). Distinct morphotypes in the structure of the protoconch were found in samples of Caspiohydrobia spp. from the Caspian and Aral Seas. Although the characteristics of the protoconch (size, sculpture) do not give grounds to distinguish ‘good’ species within the group, the genetic and morphological diversity described in this work makes it possible to assume the ongoing microevolutionary processes within the discussed group and, possibly, the existence of young (incipient) species in Central Asia. Based on the study of the morphology of the protoconch, it has been suggested that the development of molluscs of the genus Caspiohydrobia (= Ecrobia, partim) can include the free-swimming larval stage; this hypothesis is, however, not supported by other evidence and needs to be carefully verified.

By sequencing ISSR DNA fragments of the Austrian snail (Caucasotachea vindobonensis), cloned into the pAL2-T vector, sequences of microsatellite loci (STR) and their flanking regions were obtained. For the nine identified STR loci with 2, 3 and 4 repeats, the design of primers adapted for fragment analysis was carried out. Subsequent genotyping of 100 individuals of the Austrian snail from various populations of Eastern Europe to estimate the volume allelic diversity of the species based on detected STR loci. All loci yielded unambiguous genotypes. Eight STR loci turn out to be polymorphic and have from 2 to 19 alleles.The data obtained can be used to assess the genetic diversity and phylogenetic analysis of populations of the Austrian snail, listed in the Red Book of the Belgorod region of Russia and the protection lists of Europe.