Crustaceans

The term crustacean comes from the Latin word crusta meaning "crust, shell, or hard surface." There majority of crustaceans are aquatic, and most of these are marine; very few are terrestrial and the most commonly known are woodlice and tend to live in damp places such as woodlands and gardens. Of the few freshwater crustaceans in Wiltshire the most well known are the native White-clawed Crayfish and the introduced American Signal Crayfish that is a serious threat to our native crayfish.

Crustaceans are best known for their hard external shell or skeleton called an exoskeleton which must be shed to allow the animal to grow. Once this takes place the new shell takes time to harden; during this period the animal is without its primary means of protection and is vulnerable to attack from predators, but they do have an impressive means of defence – the claws on some crustaceans is capable of exerting extreme pressure.

They also have two pairs of antennae that are used for sensing its environment, a pair of mandibles, two pairs of maxillae which are the mouth parts used for eating and compound eyes that are usually on stalks.

They live either a sessile life (where they are attached to the substrate by the head and cannot move independently) such as barnacles, or a mobile life where they can move about independently – such as crayfish that can walk several miles overground to colonise new areas, or they are parasitic and live attached to their hosts.