Class Crustaceans

An arthropod’s body is covered with a hard chitin shell that acts as an external skeleton to which muscles and legs attach. Crustaceans are mostly aquatic arthropods that breathe with gills and have two pairs of antennae. The river crayfish lives in fresh water, hides under stones by day and at dusk comes out to feed on algae, sick animals and carcasses. Its body is divided into a cephalothorax and an abdomen: the cephalothorax has long and short antennae, compound eyes on movable stalks, three pairs of jaws and 8 pairs of appendages – three pairs of maxillipeds, one pair of claws and four pairs of walking legs. The abdomen bears swimmerets, the last pair forming the tail fan. Normally it crawls on its walking legs; in danger it swims backward with its tail fan. Gills sit at the bases of the maxillipeds and walking legs, and the maxillipeds renew the water. Crayfish have separate sexes; the female carries eggs attached to her swimmerets and the young hatch in early summer. Because the chitin cover limits growth, the crayfish grows by moulting.