Volume 28

The present work is one of several planned articles on updating information on the biodiversity of malacofauna and palaeogeography of the Middle-Late Eocen Tavda Sea, which existed in the Western Siberia. Paper contains data on fossil species diversity of the family Naticidae of the Middle and Late Eocene West Siberian Sea and on drill holes. The drill holes indicate predator activity, prey of Naticidae and influence of abiotic factors on their behavior. Previously the invertebrate macro-fauna of the Eocene of Western Siberia was not studied. As a result, the biodiversity, paleogeography and paleoecology remained incompletely studied. This requires additional collecting, generalization and systematization of paleontological material.

Two species of the subfamily Moelleriinae Hickman et McLean, 1990 – Moelleria costulata (Møller, 1842) and Spiromoelleria quadrae (Dall, 1897) – have been reported from the northwestern Pacific so far. The present paper clarifies their distribution in the region based on the museum collections and newly obtained material from the northwestern Pacific. Also, one more species, Spiromoelleria maculata (Golikov et Gulbin, 1978), which previously had been considered as a member of the genus Homalopoma Carpenter, 1864 (subfamily Coloniinae), is here suggested to be a member of Moelleriinae.

New habitats of Lymnaea (Stagnicola) saridalensis Mozley, 1934 were discovered in the former riverbed reservoirs of the basins of the Khopor and Sura rivers in the Volga Upland (Penza region). The parameters of the shell and the indices of the copulative apparatus (ICA), which is used for distinguishing species, were determined. Studied populations were characterized by a significant variability of ICA (0.183 ± 0.01 and 0.276 ± 0.012).

New habitats of Lymnaea (Stagnicola) saridalensis Mozley, 1934 were discovered in the former riverbed reservoirs of the basins of the Khopor and Sura rivers in the Volga Upland (Penza region). The parameters of the shell and the indices of the copulative apparatus (ICA), which is used for distinguishing species, were determined. Studied populations were characterized by a significant variability of ICA (0.183 ± 0.01 and 0.276 ± 0.012).

Gibbinae subfamily in the Mauritius Island is represented by four taxa of generic rank. The anatomy of the type species of three of them has been known previously. The description of the reproductive tract of the fourth – Plicadomus sulcatus (Müller, 1774) is presented. It is shown that under striking conchological differences the anatomy of members of all four taxa is very similar and differs in quantitative characters only (the ratio of the length of the separate elements: the vagina / free oviduct and the relative length of the penis.). On the basis of this fact it was concluded that Mauritian Gibbinae is represented by a single genus Gibbus Montfort, 1810 with four subgenera (Gonospira Swainson, 1840, Plicadomus Swainson 1840, Gonidomus Swainson, 1840, and Gibbus s. str.).

Large population of Caucasian mollusc Harmozica ravergiensis was found in the Gvozdiv village in Kyiv region. There were no reports of this species from Central Ukraine before now and this locality is most northwestern for it. Population was monitored during the 2015-2017 and evidently survived two winters on the open grounds in this period. Shell and reproductive anatomy of H. ravergiensis from Gvozdiv are described and illustrated. The presence of the species in area is discussed. Moreover, another new finding of H. ravergiensis is reported: in Petrykivka village (Dnipropetrovsk region, Southern Ukraine) in 2016.