Crustacea.

Crabs, Prawns, Shrimps and Lobsters, but also Woodlice and Barnacles are but a few of the wonderfully diverse members of the group of organisms known as the Crustacea.

The Crustaceans are only the third largest of the great Arthropod subphylla, containing a lower number of species than either the insects or the arachnids. However in terms of diversity of form they exceed both these groups together.

This great flexibility of structure, along with the general successfulness of the Arthropod plan (exoskeleton and jointed limbs) has enabled them to be extremely successful as a group of animals. However it has also made it almost impossible to describe a typical Crustacean.