Freshwater Mollusca of Kazakhstan (Central Asia): species composition and estimation of taxonomic richness

Central Asia, including its freshwater basins, belongs to the Palearctic realm but exhibits significant faunal heterogeneity with localised hotspots of endemism. While several Central Asian countries have been the subject of malacological reviews, Kazakhstan, the largest country of the region, lacks a comprehensive and taxonomically updated species list. The aim of this study is to consolidate all available data on Kazakhstan's freshwater molluscs, critically analyse their species composition, and assess the level of endemism in this group across the country. Based on the analysis of museum collections and literature sources, we estimate the species richness of freshwater molluscs in Kazakhstan at 87 species (55 Gastropoda and 32 Bivalvia), with an expected total of 93 species. Overall, species richness declines from the forest-steppe zone in the north and northeast toward the arid and mountainous regions in the south and southwest. Six potentially endemic species were identified; however, the taxonomic status of some requires further verification. The freshwater malacofauna of Kazakhstan has been affected by recent invasions, with at least seven species classified as neo-biotic, and for some, we hypothesise a recolonisation of habitats lost during the Pleistocene.