Ischadium recurvum

Ischadium recurvum, known as the "hooked mussel" or "bent mussel," is a species of bivalve mollusc in the family Mytilidae. It can be found along the Atlantic coast of North America, ranging from Cape Cod to the West Indies. They are often found growing on Eastern oysters, either intertidal (south of Chesapeake Bay, where the exposed oysters can survive the winter) or subtidal. They also attach to other hard substrates, including artificial reefs and dead shells of brackish water clams, Rangia cuneata.