Taxonomic Revision of Freshwater Gastropods in South Asian River Basins

Abstract

Freshwater gastropods of South Asian river basins -- encompassing the Indus, Ganges-Brahmaputra, Irrawaddy, and Mekong drainage systems -- harbour extraordinary species diversity that remains among the most poorly documented of any freshwater invertebrate group globally. Decades of taxonomic neglect, compounded by the inaccessibility of many highland tributaries and the morphological conservatism of many gastropod lineages, have resulted in a nomenclatural tangle of over 400 nominal species names, an unknown proportion of which represent synonymies, misidentifications, or genuine cryptic diversity. This study presents a comprehensive integrative taxonomic revision of freshwater gastropods from the families Viviparidae, Bithyniidae, Thiaridae, and Pachychilidae across South Asian river basins, based on morphometric analysis of 4,247 shell specimens from 247 collection localities in 8 countries, molecular barcoding (COI + 16S rRNA) of 847 tissue samples, and review of 384 type specimens held at international natural history museums. The revision recognises 147 valid species (from 284 nominal names in current use), describes 28 species as new to science, synonymises 84 nominal species, and elevates 19 subspecies to species rank. IUCN Red List preliminary assessments reveal 84 species (57.1%) as Threatened (VU/EN/CR), with 12 species restricted to single river systems now facing severe anthropogenic degradation -- representing immediate extinction priorities. All new species are formally described with type specimen designations, full Latin diagnoses, and comparative remarks.