The Cumberlandian Combshell (Epioblasma brevidens) is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae. This species is endemic to the United States, found mainly in the states of Tennessee and Virginia. This mussel resides in medium-sized streams to large rivers. The combshell is an endangered species and protected under the Endangered Species Act of 1973. The combshell is threatened by habitat modifications and pollution.