Crabs are crustaceans and related to lobsters and shrimps. There are almost 5,000 different species of crabs, about 4,500 are true crabs, plus around 500 are hermit crabs (hermit crabs do not have a very hard shell and use other animals old shells for protection).
However, crabs have evolved so that they can walk or run sideways, as well as burrow and swim. The body of a crab is covered by a chitinous shell called a carapace. Find out more!