Any of various crabs belonging to a group within the order Decapoda that protect their soft unarmored abdomens by occupying and carrying about the empty shells of snails or other univalve mollusks. a kind of crab that lives in the empty shells of other sea creatures. Any crab (families Paguridae and Coenobitidae) that uses empty shells or other hollow objects as a shelter for partial containment and protection of the body. They are found worldwide in sandy-or muddy-bottomed waters and occasionally on land and in trees. They have two pairs of antennae and four pairs of legs; the first pair of legs is modified to form pincers, shaped to cover the shell entrance when the animal is inside. As the crab grows, it periodically leaves its shell and finds a larger one to occupy. The reddish brown large hermit crab (Pagurus pollicaris; 4-5 in., or 10-12 cm, long) and the small hermit crab (P. longicarpus) are found in North American Atlantic coastal waters