Additional material collected in September 2019 made it possible to clarify the range of conchological variability of Harmozica zangezurica recently described from the Syunik region of Armenia, which largely overlaps with that of Harmozica pisiformis thus rendering impossible the reliable identification of empty shells. At the same time the stability has been proven of a diagnostic feature of H. zangezurica – very long vaginal appendages whose length is approximately equal to the total length of the penis and epiphallus,. This character allows reliable distinguishing of H. zangezurica not only from the conchologically similar species H. pisiformis, but also from other representatives of the genus Harmozica. Some data on the ecology and life cycle of H. zangezurica were obtained.

Mature glochidia of freshwater bivalves can give additional features for taxonomic revisions. To study morphology of glochidia with the scanning electron microscope (SEM), special collecting techniques, storage and preparation are required. Based on extensive personal experience, an overview of various techniques is presented, both positive and negative. The interactions of chemicals used for the storage of glochidia and dissolution of glochidial tissue are described. Techniques for cleaning and mounting the glochidial shells of Unionidae for investigations by SEM are described and compared.

Studying of the demographic characteristics of populations of alien species at the stage of expansion makes it possible to assess their invasive potential. Field studies of alien terrestrial gastropods Xeropicta derbentina (Gastropoda, Stylommatophora, Hygromiidae), Brephulopsis cylindrica (Gastropoda, Stylommatophora, Enidae) and Harmozica ravergiensis (Gastropoda, Stylommatophora, Hygromiidae) have been carried out in Belgorod city, the southern part of the Central Russian Upland (Russia). All studied species are native to the Black Sea region and the Caucasus; in the southern part of the Central Russian Upland, they have been registered over the past ten years. The population density, demographic structure, and spatial structure have been analyzed for three years of observations (2017, 2019, 2020). During this period, the changes in the population density have been noted for all studied species. The most pronounced changes have been observed in X. derbentina, whose population density has significantly decreased, and the spatial structure has changed from clustered type to random distribution. In addition, the age structure of X. derbentina population had a pronounced change at the beginning of the snail activity season of 2020.

The expansion of the other two invaders, B. cylindrica and H. ravergiensis, is proved as more successful. At the same time, H. ravergiensis is distributed throughout the city. This species has stable population density and random type of spatial population structure on most sites. B. cylindrica has the highest population density: in 2020, it has reached 406 ind./m2 on average, with the maximum of 1215 ind./m2. Meantime, the species keeps the clustered spatial structure, which is explained by both high population density and adaptation to the arid conditions of its natural range.

A new species of the family Coryphellidae, Coryphella alexanderi sp. nov. is described based on specimens collected in the Kuril Islands, North-West Pacific, from the upper sublittoral to 200 m depth. An integrative analysis was conducted, including a molecular phylogenetic analysis based on four markers (COI, 16S, H3, 28S), an automatic species delimitation method ABGD, and an analysis of the external and internal morphology using light and scanning electron microcopy. The distinctiveness of Coryphella alexanderi sp. nov. is well established both morphologically and genetically, and it differs from externally similar species in radular characters. Phylogenetically Coryphella alexanderi sp. nov. is closely related to Coryphella trophina, which occurs sympatrically in the same geographic and bathymetric ranges. Coryphella alexanderi sp. nov. appears to be restricted to the middle and northern Kuril Islands, which is consistent with the high numbers of endemic taxa in this area.

On the territory of Republic of Croatia a new subspecies of land snails of the clausiliid genus Ruthenica has been found. Illustrated description is presented. New subspecies differs from other in shell shape, semi-apostrophic aperture and sculpture pattern.

Two subspecies of the schoolmaster gonate squid Berryteuthis magister (Berry, 1913) have been described to date: B. magister nipponensis Okutani et Kubodera, 1987 from the Pacific Ocean off the coast of Japan and Sea of Japan, and B. magister shevtsovi Katugin, 2000 from the Sea of Japan. The gonatid species Gonatus septemdentatus Sasaki, 1915, which was later recognized as a junior synonym of B. magister, was also described from the Sea of Japan. Comparisons among these three taxa and with the nominative subspecies using morphological and ecological features suggest that individuals of the genus Berryteuthis inhabiting the Sea of Japan belong to the species B. septemdentatus (Sasaki, 1915), which should be considered the valid name for this taxon.

The new replacement name Takashius nom. nov. is proposed to solve the homonymy between the fasciolariid genus Okutanius Kantor et al., 2018 and the hymenopteran genus Okutanius D.R. Smith, 1981.

The nominal species name “Theodoxus dniestroviensis” was commonly accepted as introduced by Put’ in 1972 for neritid snails occurring in the upper part of the Dniester River basin. Currently an earlier publication [Put’, 1957] has been found in which this name is established in accordance with the ICZN guidelines, so the dating should be amended to Put’, 1957.

The type series of Theodoxus dniestroviensis is apparently lost but the samples from the type locality were recently traced in the National Museum of Natural History of the National Academy of Sciences of Ukraine (Kiev). An illustrated comparison of topotypic specimens with other morphotypes of regional river nerites is provided. Given the variation in conchological characteristics observed among the specimens of Th. fluviatilis, we consider Th. dniestroviensis to range within its intraspecific variability. This makes Th. dniestroviensis a junior subjective synonym of Theodoxus fluviatilis (Linnaeus, 1758).

The first record of the eastern Mediterranean species Monacha claustralis in Western Ukraine is described, where it was found in one urban habitat of Lviv together with a conchologically similar Monacha cartusiana. Based on the results of our research and literature data, the reliability of some anatomical criteria that can be used to differentiate M. claustralis and M. cartusiana has been analyzed. A considerable variability in the length and shape of the vagina in M. cartusiana in Western Ukraine has been demonstrated, which may cause the erroneous identification of some specimens of this species as M. claustralis. The pattern of the present distribution of M. cartusiana in Western Ukraine are also characterized.

Boreotrophon oparini sp. nov., found in the Sea of Japan, off Russian Maritime Territory, is described and illustrated. The type material was sampled at a depth of 40 m (holotype) and 110 m (paratype) during the 64th expedition of R/V Akademik Oparin. Boreotrophon oparini sp. nov. is compared with the sympatric B. candelabrum and other congeneric species.

Examination of unsorted microgastropod samples collected during the joint Russia-German research “Sea of Japan Biodiversity Studies (SoJaBio) Expedition” in 2010 and preserved in the National Scientific Center of Marine Biology, Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, resulted in the finding of six species of the family Rissoidae. Among them, “Alvania” nihonkaiensis Hasegawa, 2014 is newly recorded both in Russian waters and on the northern slope of the Sea of Japan, and Punctulum reticulatum Golikov, 1986 was rediscovered for the first time since its original description. Geographical and vertical distributions of each species and their significance are updated and discussed.

New data on the records of synanthropic slug species of Limacus maculatus and Arion vulgaris in Belarus are analyzed. It is assumed that the penetration of these species into the territory of Belarus occurred from other parts of their modern range together with the imported goods.

In 1990 I.P. Bogdanov provided the new localities for Propebela fidicula – off the Wrangel Island in the Chukchi Sea and off the eastern coast of Kamchatka [Bogdanov, 1990]. These locations were far beyond the known range of this species – from Puget Sound Bay to the Aleutian Islands [Oldroyd, 1927]. Verification of material from the ZIN collection showed that the real Propebela fidicula in Russian waters is found only near the Commander Islands. The shells that Bogdanov identified as Propebela fidicula, belong to a new species. It differs from Propebela fidicula both in sculpture and radular morphology.

The fauna of the rivers of the north of Western Siberia that do not belong to the Ob’ River basin is of particular interest from the point of view of zoogeography and understanding of the processes of formation of the freshwater malacofauna. Starting in the taiga zone, these rivers flow north and cannot serve as a way of interzonal dispersal of species from lower latitudes. However, information about the fresh-water malacofauna of these river basins is poorly presented in the scientific literature, some of the published species findings are doubtful or erroneous. The gastropod mollusks of the family Valvatidae of the Taz river basin (Western Siberia) are considered. The basin is located closer to the Yenisei than to the Ob’ River basin. The study was based on original authors’ material represented by both qualitative and quantitative samples. It has been found that eight species of mollusks of the genus Valvata occurs in the water reservoirs and streams of the Taz basin, an annotated list of species is presented, and a brief zoogeographic characteristic is given. Three species (Valvata helicoidea, V. sorensis and V. korotnevi) are for the first time recorded from the basin, one of them (V. korotnevi) is for the first time recorded from the Western Siberia waterbodies.

The terrestrial snail genus Stemmatopsis is mainly distributed in northern Vietnam and northern Laos. In total five species of Stemmatopsis are discovered, including two described herein. Stemmatopsis arcuatolabris sp. nov. has a small distorted-ovate shell with last whorl protruded quite strongly from ventral side. It has a thickened, expanded peristome with bended palatal side having a bow-like shape. Stemmatopsis dolium sp. nov., has a small, oblique-ovate shell, an approximately quadrangular aperture, and a wave-like shape at the palatal side of peristome.

The shell colour and banding were analyzed in more than 2000 specimens of Cepaea nemoralis collected in 11 localities in Moscow and the Moscow region. In the colonies studied, snails with pink shells usually predominate, most often represented by the phenotype 00000 (complete absence of the spiral bands). In most cases, yellow unbanded shells were absent or represented by single specimens. Brown shells, almost exclusively unbanded, were found only in 5 sites. On the example of colonies from Zagoryanski and Buch (Berlin), as well as Sheremetievski and Dolgoprudnyi, the phenotypic composition of newly formed colonies and colonies that could have been their origins was compared. A decrease in phenotypic diversity of newly formed colonies was noted.

The cellular composition, the morphology of the components, and the screening function and evolutionary changes of the light-insulating apparatus of the camera-like eye of the terrestrial gastropod pulmonate mollusk Arion rufus .were studied and evaluated using light and electron microscopy. According to all the considered characteristics, the light-insulating apparatus of A. rufus is typical for terrestrial pulmonate mollusks. Evolutionary transformations of the light-insulating apparatus, caused by the change in the mollusks' environment, are insignificant and affect the cellular composition, the morphology of pigmented cells and the isolation of the light-sensitive parts of photoreceptor cells from each other.

I propose to restore the old genus name Squamophora for S. oviformis and the described herein S. nierstraszi sp. nov.. A new emendation of the genus Squamophora is provided, taking into account the main features of the shell, girdle and radula that distinguish it from the closely-related genus Loricella. The new species differs from the type species by the sculpture of the dorsal scales and the shape of the radula teeth.

The phenotypic composition of C. hortensis colonies was studied in Western Ukraine (more than 30 thousand adults from 23 settlements and 5 administrative regions) and the Moscow region of Russia (more than 500 adults and juveniles from two colonies in Moscow and Vidnoe). Most Western Ukrainian colonies were characterized by the absence of pink shells, the high frequencies of unbanded shells (70% or more), as well as the white ground colour in all banded shells. It is supposed that the latter feature makes it possible to reliably identify the colonies formed by the descendants of the primary introduction of C. hortensis into Western Ukraine, which occurred in the 20th century, from later and independent repeated introductions of this species. Unlike Western Ukraine, snails with yellow banded and pink shells were found in both colonies from the Moscow region. Pink banded shells were registered only in Moscow as well as in two colonies from Lviv. In two of the three colonies mentioned, part of the pink unbanded (Moscow) or all pink shells (Lviv) had a dark lip.

In the present work we investigated the influence of three days anoxia on hematological parameters, morphological and functional characteristics of eryhroid cells of alien bivalve Anadara kagoshimensis. Oxygen concentration in seawater was decreased by bubbling with nitrogen gas for 5 h. Temperature was maintained at 20±1oC and photoperiod was 12h day: 12h night. Extrapallial fluids were sampled by a puncture of extrapalial cavity. Three-day exposure to anoxia caused pronounced cellular responses. At the organismic level changes were not observed, as hemoglobin concentration the total number of erythroid cells and mean hemoglobin concentration (МСН) remained at the level of normoxia. We observed an increase of cellular anomalies, i.e. shistocytes and erythroid cells with polymorphic nuclei, and cells undergoing reactive amitotic division, which resulted in formation of binuclear cells. Nuclear volume (Vn) increased for more than 40 % compared to control level. This increase depended on the duration of anoxia. Changes in cellular volume (Vc) possessed a complicated manner. At the end of experimental period (3rd day of anoxia) nucleo-cytoplasmic ratio was 36% lower comparing to normoxia. Exposure to anoxia did not cause mortality of erythroid cells. The number or red blood cell shades observed on slides remained at control level.