An illustrated overview of the type series of nominal taxa of the gastropod genus Theodoxus (Neritidae) inhabiting the Ponto-Caspian region is presented. It is made on the basis of a revision of large European malacological collections and includes descriptions of the type specimens of 16 taxa of different rank (species, variety, morph). Apart of these, the “type” specimens of four taxa with unavailable names have been traced in ZIN collection; we illustrate them to show the variability of Ponto-Caspian Theodoxus. In most cases, the photographs of the type specimens are published for the first time. We provide a taxonomic analysis of all studied type series, with comments on the nomenclature, systematic position and taxonomic rank of all nominal taxa of Theodoxus recorded from the Ponto-Caspian area.

The article is devoted to the fauna of Bivalvia (family Sphaeriidae) of waterbodies and watercourses of the eastern slope of the Polar and Pre-Polar Urals. The fauna of freshwater clams of this region remains practically unexplored. This study aimed at identification of the species content of Bivalvia and publication of images of their shells. We analyzed both qualitative and quantitative samples of molluscs as well as fish stomach contents. The identification of the material was based on conchological features, including the hinge structure. In total, 31 sphaeriid species is reported, and the annotated check-list, brief zoogeographic characteristics of the fauna, and shell images are provided. Most species demonstrate a limited spatial distribution within the studied area. The causes of discrepancies between published lists of sphaeriid species are discussed.

Pontophaedusa gregoi sp. nov. is described from the Imereti Region of Georgia. This is the second species of a Tertiary relict genus that represents a very early diverged lineage of the Phaedusinae subfamily. The differences between the shell characters and climatic preferences of the Pontophaedusa species are discussed.

A new genus and species of Cepolidae are described from the Island of Cuba: Plagiosimilis gibarensis gen. et sp. nov. It is classified in Cepolidae based on the following diagnostic characteristics of the family: dart apparatus consisting of a dart sac with a pedunculated gland on its apical side, both covered by a sheath; at the base of the dart apparatus there are two accessory glands; absence of a diverticulum. The specimens from the new genus come from the northern part of the Holguin province in the vicinity of the town of Gibara and live in special habitat dominated by Tillandsia plants. Shell with the rounded last whorl last very globular round, circular umbilicus and strongly reflected lip distinguish conchologically the new genus. The reproductive system and the shell differ from the other genera, although it have a certain similarity with the genera Plagioptycha and Hemitrochus.

A report is given on the genus Rhiostoma (Cyclophoridae) collected in Vietnam during recent fieldwork. Locality data, Vietnam distribution and general distribution are given for each species, including references to previously published records. Five named species are listed, of which a new species is described, Rhiostoma ningbien sp. nov., from Dien Bien, North-western Vietnam.

The family Lyonsiellidae comprises carnivorous bivalve molluscs, distributed worldwide from sublittoral to ultraabyssal depths. One of the key anatomical characters of lyonsiellids is the reduction of the gill filaments in size and number and an increase of amount of muscles and connective tissue in gills, so their ctenidia represent an intermediate stage between eulamellibranch and septibranch conditions. The family Lyonsiellidae presently includes four genera: Lyonsiella, Allogramma, Policordia and Dallicordia. Taxonomy of the family is still problematic at both generic and species levels. The genus Dallicordia, typified by Lyonsiella alaskana was established on the assumption that it has no gills but possesses a muscular septum pierced by ostia, in contrast to the other lyonsiellids that have filamentous gills. Additionally, Lyonsiella uschakovi and Policordia ochotica were tentatively assigned to the new genus. Later P. ochotica was synonymized with P. media. In this paper we show that actually the Dallicordia was typified by an undescribed species misidentified as Lyonsiella alaskana which we describe here as D. bernardi sp. nov. Taxonomic position of the genus is dubious and could be clarified only after additional anatomical data on its type species becomes available. On the basis of examination of the type material of P. ochotica and images of the holotype of P. media, we reinstate the species P. ochotica. For the first time photographs of the holotype of L. uschakovi are provided for this specimen that was previously considered lost. Given the current state of knowledge we propose to consider species L. alaskana, L. uschakovi and P. ochotica in frame of the genus Policordia, for which we provide a list of all 29 species described up to date.

Flabellina rubrolineata was believed to have a wide distribution range, being reported from the Mediterranean Sea (non-native), the Red Sea, the Indian Ocean and adjacent seas, and the Indo-West Pacific and from Australia to Hawaii. In the present paper, we provide a redescription of Flabellina rubrolineata, based on specimens collected near the type locality of this species in the Red Sea. The morphology of this species was studied using anatomical dissections and scanning electron microscopy. To place this species in the phylogenetic framework and test the identity of other specimens of F. rubrolineata from the Indo-West Pacific we sequenced COI, H3, 16S and 28S gene fragments and obtained phylogenetic trees based on Bayesian and Maximum likelihood inferences. Our morphological and molecular results show a clear separation of F. rubrolineata from the Red Sea from its relatives in the Indo-West Pacific. We suggest that F. rubrolineata is restricted to only the Red Sea, the Arabian Sea and the Mediterranean Sea and to West Indian Ocean, while specimens from other regions belong to a complex of pseudocryptic species.

The trophic relationships between two species of symbiotic gall-forming molluscs from the genus Stilifer (family Eulimidae) and two of their hosts-asteroid species, Linckia laevigata and Culcita noveaguineae, were investigated using the stable isotope analysis of carbon and nitrogen. The aim of present study was to identify the most preferable host tissue in the symbionts’ diet. We analyzed δ15N and δ13C values in tube-feet, gonads and digestive glands of the hosts-starfishes and in muscles of the molluscs. Both symbiont species did not differ to each other both in δ15N and δ13C values. The average δ15N and δ13C values of Stilifer variabilis were significantly different from the digestive glands and gonads of their host Culcita novaeguineae and did not show differences from the tube-feet of starfishes. A similar pattern was found in the symbiotic association of Stilifer utinomi and Linckia laevigata. The tube-feet of analyzed starfishes had significantly higher average δ15N and δ13C values than the digestive glands and gonads. Obtained isotopic signatures indicate that symbionts do not feed on the host’s tissues, but take nutrients from their digestive system. It seems that the proboscis of Stilifer spp. absorbs the nutrients from the digestive system of the host-starfish thereby not disturbing significantly the host’s immune system.

Gastropod Aporrhais pespelicani was recently recorded for the first time in several localities along the Murman Coast (SW Barents Sea). In all areas, only single specimens were collected with the exception of Kislaya Inlet where the dense population was found. We repeated field study in the Kislaya Inlet decade later after the first findings of the species. No living specimens were found at the place of the previous habitat of the population of Aporrhais pespelicani, however, two adult snails were collected in a remoted locality from the same waterbody. We hypothesize that distribution of Aporrhais pespelicani in the its northern edge of range fit to “core-satellite” metapopulation model, where Murman local populations representing “satellites” of the Norwegian “core”. There is no evident proof on the relation of recent records of Aporrhais pespelicani with range extension due to the climate change, as it was suggested before.

A relict and endemic species of the Blue Nile drainage basin, the mussel Unio abyssinicus, is under the threat of extinction, with the continuing decline in the area, while data on the localities and biology of the mollusc are scarce. A new find of the mollusc population in the Duko river, located in the Oromiya Region of south-western Ethiopia, gives additional information about distribution of this species. The morphology of siphons of U. abyssinicus has been studied for the first time, the features of siphonal papillas are compared with those of the other mussel species. The data on the beak sculpture as well as the morphology of the hinge teeth have been clarified. Some new data on biology of the mussel are provided.

A new replacement name Gallardochiton nom. nov., is hereby proposed to solve the homonymy between the polyplacophoran genus Gallardoia Sirenko, 2007 and the insectean genus Gallardoia Bruch, 1924.

Description of Neofruticicola donum gen. et sp. nov. from Kugitangtau Range (Central Asia) has presented. Conchologically the new species is similar to Fruticicola perlucens (Rosen, 1901), but anatomically it represents an unique for Bradybaenidae case of partial reduction of accessory organs of female part of the reproductive tract.

Vietnam with its limestone ranges that are concentrated mainly in northern, north–central and southern parts, and many different limestone islands running along the coastline, has a phylogenetically-diverse land snails fauna dominated by endemic species. The genus Cyclophorus (Cyclophoridae) in Vietnam is studied. Sixty species and subspecies from various habitats of limestone areas throughout Vietnam are confirmed and recorded. New species and subspecies, Cyclophorus implicatus kanhoensis ssp. nov., from Northwestern Vietnam, and Cyclophorus tamdaoensis sp. nov., from Northern Vietnam are described and discussed. In this paper, the Cyclophorus courbeti var. leucostoma Dautzenberg et Fischer, 1905, is elevated to subspecies.

Unio mongolicus Middendorff, 1851 (Bivalvia: Unionidae) was described from Gorbitza mountain stream (in the east of Trans-Baikal Territory, Russia) and the taxonomy has changed over the past century and a half. A specimen of Middendorffinaia mongolica from the Gorbitza stream collected 160 years later is a match with the type illustration of Unio mongolicus from the type locality. Comparison of the shell morphology of the type specimen of U. mongolicus with the modern specimen collected from this location, combined with our analyses of molecular, anatomical and conchological data of M. cf. mongolica species from rivers of the Upper Amur River Basin and the far eastern Russia, revealed that these taxa all belong to a single polymorphic species. The molecular analysis of the COI gene fragment mtDNA of examined Comparatory Species assigned to Middendorffinaia Moskvicheva and Starobogatov, 1973 confirmed they are only intraspecific forms of M. mongolica. Morphological and genetic distances between M. mongolica and Nodularia douglasiae Griffith et Pidgeon, 1833 confirmed their assignment to two independent genera. Differences of morphologically similar species M. mongolica, N. douglasiae and Unio crassus Philipsson in Retzius, 1788 were separated based on conchological characteristics and anatomical features. History of the taxonomic changes for Unio mongolicus is discussed here.

For the first time, the widely spread Antarctic species Leptochiton antarcticus was found at the Emperor Seamounts in the North Pacific Ocean. In spite of a large distance between the Emperor Seamounts and Antarctica, the found specimen have very similar shell, girdle, radula and gill features to the type material. I propose that L. antarcticus spread to the North Pacific from the Antarctic via a deep-water current near the ocean floor, and perhaps it inhabits the slopes of islands and continents from the South Ocean to the Emperor Seamounts.

Two substitution names are proposed for primary homonyms introduced for land snail of the family Camaenidae in Thach [2018].

The genus-group taxon Elbasania Schileyko et Fehér, 2017 has recently been introduced as a subgenus of Metafruticicola Ihering, 1892 for a species occurring in north-western Greece and Albania. Using mitochondrial and nuclear markers, the phylogenetic relationships of Elbasania within Metafruticicolini (Hygromiidae) are reconstructed. The results of these analyses suggest that Elbasania is more closely related to Hiltrudia Nordsieck, 1993, which has a range adjacent to that of Elbasania from Croatia to northern Albania, than to Metafruticicola. Elbasania shares with Hiltrudia and also Cyrnotheba Germain, 1929 a very characteristic microsculpture of the shell and an overall similar genital system, which however differs among these three taxa with regard to its internal structures, especially those of the penis. Therefore, it is suggested regarding Elbasania as a distinct genus here.

The predatory family Streptaxidae is comprised of five species occurring in Thua Thien Hue Province, central Vietnam. The present paper provides an assessment of the literature data relevant to these species and the description of two new species. Haploptychius bachmaensis sp. nov. has an oblique-heliciform shell with elevated spire. The aperture is subcircular, peristome discontinuous, thick and slightly expanded, apertural dentition with one strong parietal lamella. Perrottetia namdongensis sp. nov. has a rounded and protruded shell periphery. The aperture is subcircular, peristome is discontinuous, thick and expanded, apertural dentition with one large, strong parietal lamella, one small upper palatal lamella, one large palatal lamella, one large basal lamella, and one large strong columellar lamella.

All available data and most of materials on Acicula parcelineata from Ukraine are reviewed. Thirteen areas inhabited by the species are reported for Ukraine, some of which include several known sites. Five of these areas were not reported before. Map of general distribution of A. parcelineata is provided (outside Ukraine based on published data). Habitat preferences of this species are reviewed, it occurs in Ukraine almost exclusively in forests with presence of beech, on altitude 300-1100 m. Conservation status of A. parcelineata in Ukraine is shown to be “Near Threatened” according to IUCN criterions, it is recommended to be included into the next edition of Red Book of Ukraine. Shells’ measurements of A. parcelineata are provided and compared with related Platyla jankowskiana. The later species is discussed; it seems to be possible that it represents large abnormal specimens of A. parcelineata.

In present paper, we report the first findings of two large and conspicuous nudibranch species for Russian waters - Goniodoris nodosa and Flabellina pellucida. Both species show wide distribution in the northeastern Atlantic waters or even in the northwestern Atlantic in the case of F. pellucida. The morphology of both species was studied using anatomical dissections and scanning electron microscopy. Molecular diversity was assessed by sequencing of COI marker and reconstruction of haplotype networks. In the Barents Sea, both species show minor genetic differences from their European relatives and similar morphological characters. Putative explanations of new findings for Russian Arctic are discussed.