purse crab

noun

: a large burrowing land crab (Birgus latro) that is widely distributed about islands of the tropical Indian and Pacific oceans, has a varied omnivorous diet that includes coconuts, and is related to the hermit crabs but distinguished by its large size and its broad symmetrical abdomen the oily flesh of which is esteemed as a local delicacy

called also coconut crab, palm crab, robber crab, tree crab

: any of a family (Leucosiidae) of crabs characterized by a granular carapace and long claws and by an adult female having the abdomen formed into a hemispherical cup that snaps shut against the sternum to form a brood chamber for the eggs

especially : one (Persephona mediterranea) that occurs in shallow water along the Atlantic coast of Mexico and of the U.S. as far north as New Jersey