One of the most familiar crustaceans is the Woodlouse, Porcellio scaber.
Crustaceans have three regions to the body (head, thorax and abdomen). In some forms these are not clear in the adult. They usually have a number of pairs of legs on the thorax. Some have a small number - e.g. crabs have four pairs. Generally, the abdomen also has limbs which are often involved in locomotion.
Most crustaceans are aquatic, only a small number live on land, e.g. woodlice. Other members of the group are lobsters, prawns, shrimps and barnacles. There are also many small forms, and larvae (known as Zoea), in plankton.