The Family Pinnotheridae is a group of small, marine crabs that are often found living in association with other invertebrates, such as bivalve mollusks, sea urchins, and starfish. These crabs are known for their ability to live commensally with their hosts, meaning that they benefit from the association, but do not harm their host. Synonyms for the Family Pinnotheridae include the pea crabs and sponge crabs, reflecting the different types of hosts that they are commonly associated with. Other common names include oyster crabs, mud crabs, and ghost crabs, each of which may refer to a particular species within this diverse family of crabs.