Juvenile and subadult individuals of the Painter’s mussel Unio pictorum (Linnaeus, 1788) were recorded in dredge samples from the Om’ River in the Omsk City (southwestern part of Western Siberia). Information on the size-weight characteristics of U. pictorum from the site, its abundance and biomass are given. Possible consequences of the introduction of this neobiotic species into aquatic ecosystems of the Irtysh River basin are discussed.

This study investigates the shell variability of Phenacovolva rosea, a symbiotic gastropod inhabiting octocorals, in relation to geographical location and host coral species. We analyzed shells from 53 adult specimens collected at three locations in the north of Vietnam and one in the vicinities of Nha Trang City (southern Vietnam).

To describe the shells' outlines, elliptical Fourier descriptors were applied. Based on the shell outline data, principal component analysis was performed. Additionally, height and width of P. rosea shells were measured. Only the first two principal components were effective, with the first principal component accounting for 92.8% of the variation. It closely correlated with width-to-height ratio of shells. According to dispersion analysis (ANOVA), shells in Nha Trang were significantly slimmer with longer terminal processes compared to those from the three northern locations. The coral host species also impacted shell shape when considering the entire dataset. However, this difference may have stemmed from shell variations between locations, as coral composition is not independent of location. When regional samples were analyzed separately, no significant impact of the host was detected.

The factors that differed between northern locations and Nha Trang were then discussed, along with the mechanisms underlying their influence. We suggest that predation risk, influenced by water turbidity, is greater in the clearer waters of Nha Trang. This increased predator pressure may explain the presence of long terminals on P. rosea shells found in Nha Trang, potentially providing protection against some fish predators. Furthermore, the shorter and wider shells found in northern locations may be advantageous in waters with higher current speeds, whereas the long-teminal shells with narrow apertures observed in Nha Trang may be better suited for slower currents. The climate disparity, encompassing temperature and salinity mediated through precipitation, could also potentially influence shell morphology. However, the underlying mechanism remains unclear due to the complex nature of these interactions and the scarcity of literature data.

Isolating host-specific shell shape traits from other factors proved challenging, given the close association between host species composition and location. Laboratory experiments modeling each factor independently may provide a solution to this issue.

The present study reports the first observation of Euglesa globularis peaclams attached to dragonfly nymph Aeshna juncea, and E. parvula attached to the leg of the water boatmen nymph Callicorixa sp. from the Kolyma River basin in eastern Siberia (Asiatic Russia). It has been shown that the aquatic insects may play a potential role in the dispersal of bivalves both locally within one and between different water bodies.

For the first time carnivorous bivalve mollusc Cuspidaria trosaetes Dall, 1925 was recorded in the north-western Sea of Japan. There was only one species of Cuspidaria, C. ascoldica, previously known in this region. Alive specimens of C. trosaetes were collected in the Tatarsky Strait on the continental slope on muddy sediment at the depths of 531–589 m. Stomach contents of C. trosaetes consist of foraminifers, copepods and rissoid gastropods. Cuspidaria trosaetes was selected as a type species of a monotypic subgenus C. (Nordoneaera) Okutani, 1985, which is now considered a separate genus, based on the presence of a thick shell without sculpture and with thick periostracum, as well as a short rostrum. The first obtained data on anatomy of C. trosaetes suggest its close affinity with the type species of the genus Cuspidaria, C. cuspidata. Cuspidaria trosaetes and C. cuspidata share such features as the presence of 5 pairs of septal pores, thin elongated posterior labial palps and the presence of two rows of papillae on the rim of the common siphonal sheath. Taking into account new data we propose to synonymize the monotypic genus Nordoneaera with the genus Cuspidaria.

Sequentially appearing in ontogenesis, the morphometric features of mussel Mytilus galloprovincialis larvae can serve as a basis for their species identification among the pool of larvae of  other bivalve mollusc species found in the Black Sea plankton. The study presents the photographs of live mussel larvae and scanning electron microscope (SEM) images of the larvae hinge at different developmental stages: D-veliger, veliger, veliconcha and pediveliger. There was shown the sequence of morphological changes in provinculum, as well as the shell’s size and shape changes, from the earliest straight-hinge stage of veliger up to metamorphosis. The correlation between shell height (H, μm) and shell length (L, μm) [H = 1.0022∙L–29.374; R2 = 0.9879], as well as the correlation between hinge edge length (l, μm) and shell length (L, μm) [l = 0.0009∙L2 – 0.018∙L +77,78; R2 = 0.9872] were determined for mussel larvae ranging in size from 98 to 350 µm. By employing energy dispersive X-ray spectroscopy EDS(x), the elemental composition of the larvae shell’s hinge edge at the stages of veliger, veliconcha and pediveliger was determined; and it showed the presence of calcium, carbon, oxygen, sodium and chlorine. Magnesium was detected in pediveligers’ hinge edge only.

Mytilisepta virgata was first collected as empty shells attached to plastic debris in south-western part of Peter the Great Bay (Sea of Japan), near Russian-Korean border. This species may be considered as a potentially non-indigenous species in Russian waters due to coastal warming, influence of warm-water currents and its presence in North Korean waters. A description, illustrations, data on distribution and ecology and taxonomic comments are provided.

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.

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.

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.

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 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.

In 1951, the Swedish malacologist Bengt Hubendick published a catalog of species-group names in the family Lymnaeidae proposed since 1758 [Hubendick, 1951]. This catalog included 1151 entries, with information in their type localities, bibliographic references, and the position of each taxon in the then used system. Extinct taxa were not listed. This publication is an expanded and substantially revised version of Hubendick's catalog, taking into account both all species-group names proposed for the pond snails, from 1951 to 2024, as well as a number of names once overlooked by Hubendick. The present Nomenclator contains 1557 names, for each of which a reference to the original description, an indication of the type locality, the position of the taxon in the current system, and an indication of a later publication in which a photographic image of the type is given (if such a publication occurred). In some cases, taxonomic and nomenclatural remarks are provided regarding the status of particular taxa.

A new species belonging to the Fionidae (sensu Cella et al., 2016), Eubranchus flexus sp. nov. is described based on specimens collected in Nha Trang, Vietnam, South China Sea, Indo-West Pacific, from the upper sublittoral depth. An integrative analysis was conducted, including a molecular phylogenetic analysis based on three markers (COI, 16S, H3), and an analysis of the external and internal morphology using light and scanning electron microscopy. The distinctiveness of Eubranchus flexus sp. nov. is well established both morphologically and genetically. Phylogenetically Eubranchus flexus sp. nov. represents a derived branch in the phylogeny of Eubranchus, but its relationships with other Eubranchus species are unresolved likely due to low taxon sampling. Eubranchus flexus sp. nov. is the first representative of the genus Eubranchus for the nudibranch fauna of Vietnam and for now its range is restricted only to the type locality.

Using light and scanning electron microscopy the first data on morphology of mature glochidia of freshwater bivalve Beringiana beringiana from Dalneye Lake in Kamchatka were received. Based on literature data a comparison with glochidia from other populations of this species is given. Among the Russian Far East populations of the discussed species, glochidia from the Dalneye Lake were the smallest, with shell sizes up to 287 µm and with a hook that does not exceed 1/3 of the glochidium height. Microsculpture of the outer surface of glochidia was tight-looped all over the whole valves.

Chuatienpupa megacanalis gen. et sp. nov. is described from Hoa Binh province, northern Vietnam. Chuatienpupa gen. nov. is characterized by a small, pupoid-shaped, smooth, glossy shell. Peristome with two canals; anterior canal twisted funnel-shaped, appearing as a very wide groove, opening on the basal side; posterior canal continues vertically upward and forming a wide groove, which is divided by the upper palatal plica. The operculum bowl-shaped, strongly convex, its outer surface smooth, glossy, and covered by a glaze. Both shell and opercular characters distinguish this new genus from other Southeast Asian pupinid genera. General shell morphology of Chuatienpupa gen. nov. is most similar to Pupina Vignard, 1829. However, the new genus differs in having two palatal and basal plicae, a twisted anterior canal, opening on the basal side, and a solid, bowl-shaped operculum, with outer surface dome-shaped and completely smooth.

Here we present detailed morphological and molecular comparison of the Tonicia species and ecotypes along Southeastern Pacific coast. Several specimens were examined by scanning electron microscopy and based on plates morphology we propose a new taxonomic key for identification of species and ecotypes of Tonicia. A total of 566 specimens were measured to explore morphological differences between ecotypes and ecoregions by means of multivariate analyses. Genetic distances and a maximum likelihood (ML) phylogeny were estimated using Cytochrome Oxidase I (cox1) to compare species and ecotypes. Morphometry and multivariate analyses revealed morphological differences between ecotypes in each species. However, cox1 genetic distances were low between ecotypes in both species (T. calbucensis and T. chilensis) and the ML phylogeny revealed an absence of monophyletic relationships between ecotypes in each species clades. The new key will be useful to identify Tonicia species by morphology without molecular analysis.

The work is based on a study of long-term collections of molluscs of the family Bithyniidae from the waterbodies of the Tyumen region (Western Siberia), located within the world's largest Ob-Irtysh natural focus of opisthorchiasis. Difficulties with species identifications of bithyniid snails, the first intermediate hosts of Opisthorchis, necessitate the publication of photographic images of Bithyniidae shells and an identification key based on discrete morphological characters. It has been established that 14 species of Bithyniidae belonging to five genera inhabit the Tyumen region, an annotated list of species is given, and a brief zoogeographical description is given. The most abundant species are Digyrcidum starobogatovi and Boreoelona sibirica, whereas Paraelona milachevitchi were found solitary.

A new camaenid Aegistohadra baii sp. nov., close to Aegistohadra delavayana but having smaller and more conical shell and anatomically different, was described from Yunnan, southwest China. Helix seraphinica Heude, 1889 was confirmed to be an Aegistohadra species based on structure of genital organs. Cryptozona yunlongensis Chen Y., Chen D. et Zhang, 1997 is transferred to Aegistohadra based on shell and genital characters.

Described is a new species of the genus Stenosemus from the Gulf of Alaska. It differs from the other species of this genus from the Northeast Pacific by having longitudinal undulating folds in the pleural areas of the intermediate valves, flattened, smooth dorsal calcareous corpuscules on perinotum and rectangular central teeth of radula.

On the basis of the collections of the R/V Vityaz in the Banda Sea, Indonesia, a review of the chiton fauna of the genera Belknapchiton and Leptochiton was carried out. Leptochiton commandorensis, until now known only from the northern Pacific near the Commander Islands, is here added to the four known Indonesian deep sea species. This species turned out to be with juveniles in the pallial groove. A scanning electron microscope study of the collected specimens of B. giganteus made a corrected, supplemented description of this rare species possible. The age variability of the valves shape and shell sculpture of the two collected species was studied. Particular attention is paid to the age variability of the number of micraesthetes on the tegmentum grains and the position of the mucro.