Discovery of an endemism hotspot of freshwater mussels (Bivalvia: Unionidae) in Assam, with a description of two new genera

The Indian subcontinent houses a unique fauna of freshwater mussels. Tectonic and biogeographic reconstructions indicate that this fauna represents a derivative of Mesozoic Gondwanan biota and that it arrived in Asia on the Indian Plate, using this tectonic block as a ‘biotic ferry’. Though a preliminary integrative revision of the Indian Unionidae was published recently, the level of endemism and taxonomic richness of regional assemblages are unsatisfactorily known. Here, we revise the taxonomy of freshwater mussels from the Brahmaputra River basin based on a large DNA-sequence and morphological dataset that was sampled in Assam, north-eastern India. We managed to collect and sequence topotypes for nearly all nominal species described from the region, except for Lamellidens friersoni and Parreysia smaragdites. Our phylogenetic and morphology-based research reveals that the regional Unionidae assemblage contains nine species, belonging to a single subfamily, the Parreysiinae. Seven species and three genera (Balwantia, Pseudoscabies Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao gen. nov., and Assamnaia Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao gen. nov.) appear to be endemic to the region, indicating that the Brahmaputra River may represent an endemism hotspot of global significance. Our findings highlight that this region should be considered a high-priority area for freshwater conservation management.