The Coosa moccasinshell (Medionidus parvulus) is a rare species of freshwater mussel in the family Unionidae, the river mussels. This aquatic bivalve mollusk is native to Georgia and Tennessee in the United States, and has been extirpated from the state of Alabama. It is a federally listed endangered species of the United States. This mussel is up to 4 centimeters long or occasionally larger and has a thin, fragile, dark brown or yellow-brown shell. The nacre of the shell is blue, sometimes with pink areas.