Anatomical study of five specimens of an endemic species of the Mauritius Island, Erepta odontina (Morelet 1851) showed that within one population disappearing of additional organs of the reproductive tract (epiphallic caecum, penial caecum, penial appendix, flagellum and retractor of penis) occur in four different combinations. It is significant that the shells of all five specimens were practically identical. It is assumed that the described phenomenon has a mutagenic nature and is regarded as a rare (if not unique) case of reduction (up to complete disappearance) of additional organs within one population.

It is proposed to restore the old name of the genus Terenochiton for Leptochiton norfolcensis (Hedley et Hull, 1912). We also provide a new description for the genus since the old description does not reflect the main features associated with the development of the articulamentum. All valves of the genus have rudimentary unslitted insertion plates. Similar rudimentary insertion plates have evolved independently in different families of the primitive chitons.

An annotated and illustrated check-list of species of the subfamily Sphaeriinae (family Sphaeriidae) of the Kama region (the Middle Urals, Russia), with enumeration of species’ localities, is presented. After examination of own collections and critical assessment of literary data, 8 species from two genera (Musculium and Sphaerium) have been included into the final list. One of these species, Sphaerium asiaticum, is recorded for the first time from the studied area. The ecological characteristics of all species as well as remarks on their distribution within the region are provided. From the zoogeographical point of view, the most sphaeriine species of the studied area belong to the European-Siberian faunistic group.

The recent record of Xeropicta derbentina in the south of the Central Russian Upland (Belgorod Region, Russia) provides the opportunity to study the alien populations structure at the stage of colonization of a new territory. High intra-and interpopulation variability of the X. derbentina shell in different parts of the range is revealed. Based on the allozyme and PCR-ISSR analysis, it was established that native and adventitious populations of X. derbentina had the same level of genetic variability. The potential number of multilocus genotypes calculated for the Belgorod population indicate a further complexity of their genetic structure. The result of the ISSR analysis showed significant genetic differentiation (FST=0.746; p=0.01) of two adventive populations from the Belgorod Region, which indicates their different origin from the natural area.

The taxonomic position of the genus Culmenella within Hygrophila remains uncertain. The spermatozoa of Culmenella rezvoji, a species from the Far East of Russia, were examined using a combination of light, scanning and transmission electron microscopy with the objective to assess the utility of sperm characters for clarifying the phylogenetic relationships of the genus. The spermatozoa of C. rezvoji are divided into four regions: head, midpiece, glycogen piece and endpiece. The head contains a slender, cone-shaped acrosome and a conical nucleus with a sinistrally coiled keel. The acrosome consists of an apical vesicle and a thick-walled pedestal with an electron lucent canal partially filled with a patchy electron-dense material. The midpiece contains the mitochondrial derivative that encloses apically three parallel glycogen-filled tracts (helices) positioned in such a way that in the sperm cross section two helices lie opposite each other and equidistant from the third helix. The surface of the sperm above one of the helices forms a high, narrow ridge; the ridges above the remaining two helices have a much lower profile. The boundary between the midpiece and glycogen piece is demarcated by a constriction (annulus) consisting of an anterior electron-dense ring and a posterior conical cylinder connected to the ring with thin filaments. The structure of spermatozoa in Culmenella is consistent with the general pattern of sperm morphology common to all studied species of Hygrophila, but the spermatozoa of Culmenella also have distinctive characters (three glycogen helices and high-profile surface ridge in the apical portion of the midpiece) that should be potentially useful in resolving the taxonomic position of this genus.

This paper provides reliable data on the occurrence of bivalve mollusk Neaeromya compressa in the Sea of Japan. Nine alive specimens (L = 5.9–19.2 мм) were collected in June 2003 in Peter the Great Bay (southern Primorye) at the depths of 66–74 m on mud and sand. These are illustrated and described in detail. The data on ecology and geographical range of the species are summarized.

The SEM image and description of the Boucardicus leopardus radula is presented for the first time. The radula appeared morphologically similar to those of representatives of Alycaeidae. At the same time representatives of Boucardicus differ significantly from South-East Asian Alycaeidae. It is suggested, that presently Boucardicus is not monophyletic and includes representatives of different genera and possibly families.

Oospira haivanensis sp. nov, a new member of the Clausiliidae subfamily Phaedusinae is described from the Hai Van Mountain in central Vietnam. The relationship of the new species to other taxa of the genus and  the zoogeographical importance of Oospira species in Southeast Asia are discussed.

The population structure of the terrestrial mollusk Fruticicola fruticum (Gastropoda, Pulmonata, Bradybaenidae) in different landscapes of Eastern Europe on the basis of conchological measurements, including morphometric parameters and color variants was studied. For all morphometric parameters used, statistically significant differences were found between the studied populations. At the same time, the shell size are determined not by zonal characteristics, but by microbiotopic conditions. Changes in the frequency of shell phenotypes in Fr. fruticum populations are probably of a multifactorial nature. The ratio of different color variants can be caused by the influence of radiation, cyclic fluctuations of climatic factors, succession changes in biotopes, and gene drift.

Two new species of the genus Callochiton are described: C. sonchaensis sp. nov. from Vietnam and C. tongaensis sp. nov. from Tonga. They differ from other congeneric species in having a different number, shape, size and arrangement of grooves on the pleural areas of the intermediate and tail valves, the number of slits, the size of the dorsal spicules, and sometimes the coloration of the girdle. Absence of Callochiton in the Caribbean Sea and along the coasts of Central and North Americas was, perhaps, due to late advancement of species from this genus into the Tethys from the regions near Gondwana.