A new endemic freshwater mussel (Bivalvia, Unionidae) genus and species, Ligodontaobscura, from the Yadkin-Pee Dee River drainage in North Carolina, USA.

We describe a new genus and species of freshwater mussel, Ligodontaobscura gen. et sp. nov., using an integrative taxonomic approach consisting of morphological, genetic, biogeographic, and life history information. Specimens of L.obscura are poorly represented in historic collections and were infrequently collected; additionally, the species was originally overlooked as a unique taxon due in part to its small size and superficial morphologic similarities to Lasmigonasubviridis (Conrad, 1835) and Alasmidonta spp. Phylogenetic results place the new species sister to, but consistently distinct from, Alasmidonta s.s. We offer a suite of field-ready diagnostics to differentiate L.obscura from similar and co-occurring species and briefly discuss the species' unique phylogenetic placement, which warrants the recognition of a new genus. Importantly, L.obscura appears to be a "microendemic" species with a remarkably limited documented range of approximately 13 km within two small, adjacent watersheds of the Yadkin-Pee Dee River drainage. Despite intensive surveys, the extant population is currently known from an approximately 7 km contiguous reach of one stream, making this newly-discovered species a high conservation priority.