Some oysters contain live crabs, known as oyster crabs.

Since oyster crabs are considered a food delicacy they may not be removed from young farmed oysters, as they can themselves be harvested for sale.

In the north Atlantic Ocean, oyster crabs may live in an endosymbiotic commensal relationship within a host oyster.

The oyster crab, Zaops ostreus, is a small, whitish or translucent crab in the family Pinnotheridae.

Many species formerly in Pinnotheres have been placed in new genera, such as Zaops ostreus (formerly Pinnotheres ostreus), the oyster crab.

Little is known about the pea crab's feeding habits, but in the related oyster crab (Pinnotheres ostreum) larval stages feed on plankton brought in by the oyster, while adults feed by taking the food that are a part of the oyster's diet as well as those that are not.