Crab (Louise Docker / CC BY)
Crabs are characterized by a pair of claws, a thick external skeleton, and a reduced abdomen, usually hidden under the thorax. They have eight robust legs, which are well adapted for walking on the seafloor. Unlike lobsters, crabs typically walk sideways. Their sizes range from a few millimeters in width (pea crab) to 4 meters (13 feet, Japanese spider crab).