The freshwater mussel fauna of Manipur (North-East India) represents a tectonically derived mixture of endemic species and (sub)recent immigrants from adjacent basins

The Indian Subcontinent houses a unique assemblage of freshwater mussels shaped by tectonic history and regional biogeographical processes. This study employs an integrative taxonomic approach, combining morphological analyses and multi-locus molecular data (COI, 16S rRNA, and 28S rRNA gene fragments), to revise the systematics of freshwater mussels from Manipur, a northeastern Indian region characterized by diverse topography and complex river systems. Six unionid mussel species within the subfamily Parreysiinae, spanning four genera—Indonaia, Lamellidens, Parreysia, and Radiatula—were identified, including the description of two new species: Indonaia manipurensis sp. nov. and Parreysia imphalensis sp. nov. The taxonomic status of Radiatula theobaldi (Preston, 1912) stat. rev., endemic to Manipur, was clarified based on newly sequenced topotypes. Our time-calibrated phylogenetic reconstructions reveal broader biogeographical patterns linked to plate tectonics, with divergence times tracing back to the Cretaceous. The origin of Parreysiinae aligns with the breakup of Gondwana, and subsequent dispersal and vicariance events during the Cretaceous to Miocene shaped their current distribution. The Manipur fauna represents a mixture of endemic and allochthonous unionid species, reflecting historical connections between freshwater systems of the Indian Plate and the Burma Terrane. Significant threats from recent human-driven activity underscore the urgent need for conservation strategies.