Volume 22

This paper presents the first data on seasonal quantitative dynamics of Gastropoda - dominant group of macrozoobenthos in three hydrodynamically different stony littoral areas of Lake Baikal. These studies were performed on the western shore of Southern Baikal (Cape Beryozovy) for 13 months in spring-autumn of 2002-2004. Species composition of gastropods varied with depth (1-20 m) from 10 to 17 species. Five species constantly inhabited the inshore area (depth 1-2,5 m), whereas in the wave-cut area (3-5 m) and the area of wave weakening (7-20 m) there were detected 6 species. During most of the investigation period, total density and biomass of gastropods was higher in the wave-cut area than that in two other regions of the lake. The rise of density and biomass of mollusks was recorded at all depth zones in autumn, whilst their quantitative values varied during other seasons. The main contributors to the total abundance of gastropods were Maackia herderiana and Choanomphalus maacki in the inshore area, whereas in the wave-cut area and area of wave weakening one species Maackia herderiana. Seasonal and inter-annual fauna dynamics of littoral gastropods was determined from changes in quantitative characteristics of species-dominants.

The structure of the distal parts of the reproductive system of the majority of the species of the genus Helicopsis occuring in Crimea and Black Sea Lowland (H. retowskii, H. dejecta, H. striata) were studied. The special attention was given to the intraspecific variability of the penial papilla shape and some proportions of the genitalia. Basing on the anatomical characters, the wide range of the conchological variability of H. retowskii has been shown. The area of this species goes out from limits of the Crimea. It is suggested that H. paulhessei (=H. gasprensis) and Xerophila elata are the synonyms of H. retowskii. The key for the determination of the Crimea molluscs of the genus Helicopsis on the anatomical characters is provided.

Anatomical study of the species described as Bradybaena boevi Uvalieva, 1967 has shown that this species does belong to the genus Bradybaena (Fruticicola in current sense). The contradictions in the literature, are related to the errors in the original description, in particular, Uvalieva took penial retractor for the flagellum.

An Illustrated description of the shell and reproductive tract of Pyramidula kuznetsovi is given. The presence of a distinct peripheral angle distinguishes this species from all known species of the genus. Both anatomically studied specimens had well-developed embryos in the uterus, whereas distal parts of the male section of reproductive tract were much reduced. Therefore it is hard to judge about anatomical differences of P. kuznetsovi from other species of the genus, in particular, the question on the presence of penial caecum remains open.

Terrestrial mollusk Laciniaria plicata from the family Clausiliidae was discovered in Penza forest-steppe territory in 2010-2011. Now it is the eastermost population of the species.

Thesbia nana is recorded for the first time in the Russian part of the Barents Sea. The species was previously known from the North Atlantic with reported Eastern distribution limit in Finmark. The brief species description is provided.

The genus Plicifusus Dall, 1902 has been revised on the basis of available anatomical data. 13 valid recent species are recognised, for 9 of them detailed descriptions of anatomy are provided. 4 names were synonymized: Plicifusus obtusatus Golikov, 1985 = Plicifusus maehirai Tiba, 1980; Colus okhotskana Tiba, 1973 = Plicifusus elaeodes (Dall, 1907); Tritonofusus (Plicifusus) aurantius Dall, 1907 and Plicifusus (Aulacofusus) rhyssoides Dall, 1918 = Plicifusus rhyssus (Dall, 1907). Plicifusus parvus, Tiba, 1980 and Plicifusus saginatus Tiba, 1980 are considered as junior synonyms of Retifusus roseus (Dall, 1877). Plicifusus laticordatus (Dall, 1902) excluded from the genus Plicifusus.