The Tar River spiny mussel or Tar River spinymussel (Elliptio steinstansana) is a species of freshwater mussel in the family Unionidae, the river mussels. This species is endemic to North Carolina in the United States. This species is endemic to North Carolina in the United States. It is expected to become extinct without significant human intervention. Under the Endangered Species Act, this species is listed as endangered in the United States.