Simpsonaias ambigua (salamander mussel) is a small-shelled member of a monotypic unionid genus and the only freshwater mussel reported to be an obligate parasite of amphibians. Recent surveys of the Duck River drainage found no historical or recent records of the salamander mussel, but documented records for 73 other species, including 53 extant taxa. In 2003, a fresh-dead shell of S. ambigua was collected from the Duck River in Humphreys County, TN. Additional specimens were found in June 2005. These specimens represent the only known occurrence of S. ambigua in the Duck or Tennessee River drainages and may represent the only remaining Tennessee population.