Porcelain Crabs (Petrolisthes eriomerus, Petrolisthes cinctipes)

There are two species of porcelain crabs that are very similar in appearance: Petrolisthes eriomerus, which goes by the names flattop crab, flat-topped crab or just porcelain crab, and Petrolisthes cinctipes, which goes by the names flat porcelain crab,smooth porcelain crab, and just porcelain crab.

Photo 1: Porcelain crab in a clam shell.

This crab is extremely flat.  I believe this particular crab is Petrolisthes eriomerus, but I could be mistaken as I didn't make a proper identification at the time. Spots at the thumb joints and coloration of mouth parts are one way to distinguish the two species: Petrolisthes eriomerus typically has blue spots and coloration, whereas Petrolisthes cinctipes typically has red spots and coloration. Unlike other crabs, which have five pairs of legs, porcelain crabs have only four pairs of legs.  (Taken at Shelter Point Reef)

Photo 2: Relative size of porcelain crab.

These crabs are  relatively small as seen in comparison to my index finger and thumb. They are also very fragile. If you grab one of the crab's legs, it will shed its leg to escape. In time, the leg will grow back. This fragile nature is supposedly the reason behind its name, but I couldn't find any authoritative source for verification. (Taken at Shelter Point Reef)

Other Pacific Northwest Crabs: Black-clawed Crab, Red Rock Crab, Kelp Crab