sand crab, crabs

True crabs have five pairs of legs, the first of which are modified into a pair of claws and are not used for locomotion. In all but a few crabs (for example, Raninoida), the abdomen is folded under the cephalothorax in the adult stage. The mouthparts of crabs are covered by flattened maxillipeds, and the front of the carapace does not form a long rostrum. The gills of crabs are formed of flattened plates ("phyllobranchiate"), resembling those of shrimp, but of a different structure. They can also be the size of a pea, or even smaller.