Raninidae is a family of unusual crabs, taken by most scientists to be quite primitive. These animals closely resemble the (unrelated) mole crabs, due to parallel evolution or evolutionary relay. In both groups, the claws are modified into tools for digging, and the body is a rounded shape that is easy to bury in sand. Unlike most other true crabs, the abdomens of raninids are not curled under the cephalothorax.