Geukensia demissa

Geukensia demissa is a species of mussel, a marine bivalve mollusk in the family Mytilidae, the true mussels. This species is native to the Atlantic coast of North America. The common names for this species include ribbed mussel, Atlantic ribbed marsh mussel and ribbed horsemussel. However, the common name ribbed mussel is also used for the Southern Hemisphere mussel Aulacomya atra. The appearance of the shell is grooved and oval in shape. The interior of this mussel is tinted purple

The ribbed shells of this species usually attain a length of 10 cm length, and can be as large as 13 cm. Age can be determined by counting dark growth rings on the shell and mussels typically live 10 – 15 years, but more advanced ages are not uncommon.