Since the last comprehensive overview of the Czech and Slovak mollusc fauna, released in 2013, several records of species new for the countries or particular regions have appeared. In this paper, we summarize all such records and news collected in 2015–2019, including those affecting nomenclature and the national Check-lists made in 2013 and 2014. The rules for the selection of the records are: (i) the first record in Bohemia, Moravia or Slovakia, (ii) regionally important new records, (iii) records of species listed in NATURA 2000 and the national Red-lists as either critically endangered or endangered species, and (iv) currently spreading non-native species. New records are briefly commented and summarized for each species separately. Location data are published with all details in a supplementary table and are freely accessible.

In this paper we provide a new list of all the mollusc species recorded outdoors in the Czech and Slovak Republics. This work is a supplement of the Ložek’s key on molluscs of the former Czechoslovakia. For the species recorded after the publishing of the book, publications of their first records in the Czech and Slovak Republics are given. Species which are either not included in this Ložek’s book or whose current taxonomical status highly differs from that published in the book are supplied with Czech commentaries, photographs of their shells or bodies, and drawings of important identification characters. This material is aimed at Czech and Slovak malacologists to provide information, missing or scattered in the literature, on currently known mo­llusc fauna of the Czech and Slovak Republics. The Ložek’s book and this supplement should provide necessary information on identification, ecology and also distribution of all mollusc species currently known from the Czech and Slovak Republics. If the species names used in this paper differ from the ones used in the Ložek’s book, we mention both. So far 247 species of molluscs, including 219 species of gastropods (50 aquatic and 169 terrestrial) and 28 species of bivalves, have been found outdoors in the Czech Republic. The fauna of Slovakia comprises 247 species, including 219 gastropods (51 aquatic and 168 terrestrial) and 28 bivalves. Altogether 282 species occur in the Czech Republic and Slovakia, 212 of them being common to both countries.

Lymnaea palustris and L. fuscus are members of the European stagnicolines (Gastropoda: Lymnaeidae). The role of stagnicolines in transmission of Fasciola hepatica has been often proposed. To assess the possible relationship between these two stagnicolines and F. hepatica in Sweden, field monitoring in parallel with experimental infections of L. palustris and L. fuscus were conducted.

A living population of Tanousia zrmanjae (Brusina, 1866) was found in the mid section of the Zrmanja River in Croatia. The species, found only in the freshwater part of the river, had been regarded as possibly extinct. A few collected specimens were used for this study. Morphological data confirm the previous descriptions and drawings while molecular data place Tanousia within the family Hydrobiidae, subfamily Sadlerianinae Szarowska, 2006. Two different sister-clade relationships were inferred from two molecular markers. Fossil Tanousia, represented probably by several species, are known from interglacial deposits of the late Early Pleistocene to the early Middle Pleistocene of several European countries. Thus T. zrmanjae may be regarded as a living fossil restricted to the short section of the Zrmanja River.

This paper presents important faunistic records conducted in the Czech and Slovak Republics during 2021. In the Šumava Mts, South Bohemia, a hydrobiid snail of the genus Alzoniella was found. Monacha cantiana s. lato was genetically confirmed for the first time in the city of Bratislava, Slovakia. New sites of Cornu aspersum (Prague) and Tandonia kusceri (southern and central Slovakia) were confirmed. A new colony of the slug Limacus maculatus was found in SE Moravia. New records of several endangered species, e.g. Vertigo angustior, V. moulinsiana, Anisus septemgyratus, Gyraulus acronicus, G. rossmaessleri, Planorbis carinatus, Pisidium amnicum, P. globulare, P. moitessierianum, P. pseudosphaerium and P. tenuilineatum, are also presented. Location data are published with all details in a supplementary table.