Some crustaceans that look somewhat like crabs belong to the Anomura. They differ from true crabs by having at most only three pairs of walking legs instead of four. Some anomurans are hermit crabs which have a soft coiled abdomen protected by a snail shell. Most hermit crabs are scavengers on dead plant or animal matter. Hermit crabs are divided into families partly on which of the two claws is bigger. Other anomurans are the false crabs, flat and with similar sized chelipeds. The abdomen is a short flap tucked under the thorax and there are only three pairs of walking legs.