Geukensia granosissimaGeukensia granosissima, common name the southern ribbed mussel, is a species of saltwater mussel, a marine bivalve mollusk in the family Mytilidae, the mussels.DistributionThis species is native to the Atlantic coast of North America. Southern ribbed mussels are found in the Florida Keys, the Caribbean and the Gulf of Mexico. On the Atlantic coast to the north, the closely related ribbed mussel Geukensia demissa is found.DescriptionThe ribbed shells of this species attain a length of 10 cm.