The group of crustaceans we are most familiar with is the decapods. This term refers to the 'ten feet' or, rather, limbs of these types of crustacean, being the two front pincers and usually four pairs of walking legs. Decapods include more than 20,000 living species, which encompass shrimps and prawns - two common names that have no strict scientific basis - along with all types of crayfish, lobsters and crabs, as also shown on the previous pages.