Sand dollar
Living sand dollars look rather different from the white tests found on the beach.
Scientific classification
Domain:	Eukarya
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Echinoidea
Superorder:	Gnathostomata
Order:	Clypeasteroida

The Sand dollars are species of flattened, burrowing sea urchins belonging to the order Clypeasteroida. Echinarachnius parma, the Common Sand Dollar, is widespread in the Northern Hemisphere, from the intertidal zone to considerable depths. Sand dollars can be found in temperate and tropical zones, but not in Great Britain.^p76

All sand dollars have a rigid skeleton known as a test. This is the typical white disk found washed up on beaches. The living animals have a skin of movable spines on the test. Movement is done by the action of the spines. Like other sea urchins, sand dollars have five paired rows of pores. The pores are arranged in a petal-like pattern. These pores are perforations in the endoskeleton through which the tube feet, used in gas exchange, project from the body.