Rare European species Pupilla pratensis is registered in the same calcareous fen in the Crimean Mountains, where Vertigo moulinsiana, another rare European species, was found earlier. Both species are known in Ukraine only from this one small site (less than 0.01 km2), which is disturbed and not protected, therefore both species are clearly “Critically Endangered” here. In the materials of Pupilla muscorum from Ukraine there are some unusual large specimens with shell width 1.9-2.0 mm were revealed, therefore these two species can’t be distinguished only by this characteristic, how it was partly considered before.

The spectral sensitivity of the eye of a gastropod pulmonate mollusk Radix peregra (Müller,1774) was investigated on the basis of phototaxis in the laboratory conditions. The monochromatic light of tendifferent wavelengths in diapason 400-600 nm servedas a test stimulus. According to the results obtained R. peregra has monochromatic visual system with a possible visual pigment rhodopsin, that may be based on the retinal A and absorption maximum of which falls on a blue-green range of the spectrum about 490 nm.

The visual acuity of a gastropod pulmonate mollusk Radix peregra (Müller, 1774) was estimated on the basis of phototaxis in the laboratory conditions. White cards with black vertical stripes of different angular width were used as visual stimuli. A value of the resolving angular distance of photoreceptors was 1-2°, and the calculated on its basis visual acuity -33-16.5 rad-1. The mollusc has a diurnal type of activity and lives at well-illuminated surface patches of ponds on aquatic caulescent plants that it feeds on. The results of behavioral investigation presented in this work and morpho-optical study of the eye carried out earlier allow to consider that R. peregra can identify caulescent plants, suitable for its inhabitation, feeding and travelling to the water surface.

В лабораторных условиях определен знак фототаксиса брюхоногого легочного моллюска Radix peregra (Müller, 1774). R. peregra показывает положительный фототаксис, который согласуется с его дневным типом активности и высоким уровнем освещенности мест обитания. Положительная реакция на свет обеспечивает моллюску нахождение мест обитания с благоприятными для жизнедеятельности световыми условиями и реализацию функции дыхания.

Anatomical study has shown that the species described as Helix duporti Bavay et Dautzenberg, 1908 belongs to the genus Trachia Martens, 1860. A brief discussion of the problems of the taxonomy of snails having helicoid shells in the fauna of Vietnam.

The problem of generic and subgeneric rank in Ariantinae is briefly discussed. A review of existing views on the system of non-helicine Helicidae (Ariantinae, Murellinae, and Thebinae) and differential diagnoses of the taxa are presented. Special attention is paid to the morphology of the atrial stimulator and, especially, penial papilla, because these organs play an important role in evolution of helicoid groups, providing the functioning of a pre-copulatory isolating mechanism.

The information on reproductive characteristics of more than 100 species of the pulmonate molluscs (clutch size, egg size, hatching success, etc.) is summarized. It is shown that the pulmonates demonstrate a very wide range of reproductive strategies that serve to enhance the survival of species in different (sometimes very unfavorable) environmental conditions.

The intricate history of Trophon birileffi Lischke, 1871 is analyzed. A lectotype is designated from 36 syntypes discovered in the Zoological Institute of the Russian Academy of Sciences in St. Petersburg, Russia. The species is redescribed and other specimens as well as the protoconch and the radula are illustrated. Two species, Sistrum alfredensis and Fusus pachyraphe formerly considered as synonyms of Trophon birileffi, are removed from its synonymy.

Carl Agardh Westerlund (1831–1908) was a prominent Swedish malacologist, who studied taxonomy and distribution of continental molluscs (terrestrial and freshwater). He established a number of new taxa, some of them are still accepted as valid. In this study, we provide information on type materials of 41 species of freshwater snails introduced by Westerlund and accepted in the current Russian taxonomy. The study is based on examination of materials from original Westerlund’s collection dispersed now among three large scientific institutions (Göteborgs Naturhistorska Museum, Swedish Museum of Natural History, and Zoological Institute of the Russian Academy of Sciences). For each species an account containing all relevant information on its type series is given. Taxonomic and nomenclatorial notes are also presented. For the majority of taxa, shells of type specimens are illustrated. The lectotypes for Limnaea truncatula var. sibirica Westerlund 1885, Planorbis dispar Westerlund 1871, Planorbis concinnus Westerlund 1881, Planorbis stroemi Westerlund 1881 and Physa sibirica Westerlund 1881 as well as the neotype for Planorbis borealis Lovén in Westerlund, 1875 are designated here.