The sperm ultrastructure of Yoldia notabilis Yokoyama, 1922 and Y. keppeliana Sowerby, 1904 was examined. Sperm cells of Y. notabilis and Y. keppeliana have classic morphology: they consist of a spherical head, midpiece and a flagellum the head consists of the acrosome and the nucleus, the midpiece containing spherical mitochondria and centrioles. Average dimensions of Y. notabilis sperm head are 3.6 μm and 2.8 μm (length and width), Y. keppeliana — 3.8×2.6 μm. Periacrosomal material of both species is poorly developed. The basic difference between Y. notabilis and Y. keppeliana sperm cells is the number of mitochondria: Y. notabilis has 5 or 6 and Y. keppeliana — only 5. A slight difference of the sperm cells in the head form and in the number of mitochondria may indicate the recent separation of the species, probably as a result of reproductive isolation.

The author presents the results of the study on intrapopulation variability in the egg cluster morphology of Planorbarius corneus (Linnaeus, 1758) in a small lake near Smolensk. The changes in the basic characteristics of syncapsules are very considerable. The most constant feature is the egg capsule size, but its limits and mean values also vary both in one specimen and in different molluscs and coincide with the variation within the genus Planorbarius Dumeril, 1806. Thus, the use of characters of egg clusters for recognition of species is impossible.

The structure of egg-clusters of two Siberian species of the subgenus Stagnicola (genus Lymnaea) is described for the first time. These are L. terebra (Westerlund, 1884) and L. likharevi Lazareva, 1967. Morphological peculiarities of egg-clusters of all Recent sections of Stagnicola are discussed. It has been shown that species of the section Ladislavella B. Dybowski, 1913 differ significantly in these features from other sections of the subgenus. It is an additional evidence for a certain taxonomic isolation of this group that was revealed earlier by means of karyologic analysis [Garbar, 2001, 2003] and DNA sequencing [Meier-Brook, Bargues, 2002; Bargues et al., 2003].

Processes of reproduction in mollusks are supported by many neuropeptides including the conopressin. During ethological and pharmacological investigation of reproductive functions of the conopressinergic system in the pond snail Lymnaea stagnalis we revealed its stimulating effect only on the egg laying, with no effect, however, on the copulation behavior. Exogenous conopressin provokes egg laying within 24 hours. Action of the peptide is realized through the conopressin receptors since antagonists of these receptors prevent egg laying. It is revealed that the action of conopressin is species-specific for reproduction behavior because a related peptide, namely vasopressin, does not affect the process of reproduction in Lymnaea stagnalis. Thus, one of the functions of the conopressinergic system of Lymnaea stagnalis is to start the female reproduction behavior.

Roman snail is a valuable food resource, which has only recently came into use in food industry in the Kaliningrad Region. To establish the rational basis for its commercial use, it is necessary to gather data regarding biological and ecological features, mostly reproductive properties of the populations which inhabit this territory. The present investigation has been carried out to study the reproductive biology of the Roman snail over a 4-year-period, with a full-range analysis of the data obtained. Reproductive peculiarities are considered for the populations inhabiting different environmental and geographical areas of the region. It became possible to identify the life conditions of the local populations of H. pomatia.

The copulation has been studied in three Clausiliidae species [Cochlodina laminata (Montagu, 1803), Laciniaria plicata (Draparnaud, 1801), Bulgarica cana (Held, 1836)] from the Tula Region. All the observed snails exchanged the spermatophores. Each snail acted as a functional male and female in sequence, changing its role during the copulation. Spermatophore structure of these species is described. Cochlodina laminata reproduces during the entire warm season and deposits eggs on the fourth day after copulation at room temperature.

Structural peculiarities of male reproductive tract of Cochlicopa lubrica (Müller, 1704) enable to assume that reproduction takes place all over the warm period. The male genitalia condition referred to as lubrica-type is a spermatogenesis (male) phase. Spermatophore of Cochlicopa lubrica is described. Anatomical investigation confirms that C. repentina is a synonym of C. lubrica.

New subgenera, Sagarmathia subgen. nov. (gen. Anadenus) and Vietanadenus subgen. nov. (gen. Anadeninus) and three new species, Anadenus (Sagarmathia) kuznetsovi sp. nov., Anadeninus (Vietanadenus) sapaensis sp. nov., and Anadeninus (Neoanadenus) susannae sp. nov. are described.

Two size groups comprised stocks of the Japanese common squid (Todarodes pacificus) migrating in the Pacific Ocean off the Kuril Islands and eastern Kamchatka in June-September 2004. Small-sized squid were juveniles while large-sized animals were adults. Juveniles occurred in June-July, and had a mean dorsal mantle length (DML) of 76 mm. Mean DML of adult squid increased northeastward from 156 mm in June to 174 mm in July off the Kuril Islands, and 239 mm in September off eastern Kamchatka. In autumn, one individual was caught as far north as 55°N, which is the northernmost point of the species occurrence reported so far, and another one to the east of the Commander Islands, in the Bering Sea (Near Strait). All adult animals were immature and were intensively preying, mainly upon fish (primarily, Myctophidae), to a lesser extend crustaceans (primarily, Euphausiacea), and occasionally cephalopods (identified as conspecific juveniles). Our findings suggested that under certain conditions, particularly, in years of intensification of the Kuroshio Current and at high stock abundance, schools of the Japanese common squid may be widely distributed in the northwestern Pacific Ocean, and may even migrate as far to the north as the area adjacent to the Commander Islands during forage migrations.

Widely used name Mytilus coruscus Gould, 1861, a common mussel in north-western Pacific, appeared to be a junior synonym of Mytilus unguiculatus Valenciennes, 1858. According to the article 23.9.1.1 of ICZN, the name M. coruscus is qualified as nomen protectum.