What is a sand dollar? What does a sand dollar look like and what do they eat? Information and facts about sand dollar.
Sand Dollar; any of a group of flattened circular invertebrate animals that are found in shallow coastal waters, usually just beneath the surface of the sand. They are also sometimes known as sea cakes.
Sand dollars are classified in several genera of the class Echinoidea of the phylum Echinodermata. They are closely related to sea urchins and to starfish.
Sand dollars may be as small as 0.5 inch (1.2 cm) in diameter, but most are usually from 2 to 4 inches (5-10 cm) across. The body is enclosed in a limy shell, known as a test, through which protrude ambulacral, or tube, feet and many very fine spines. On the aboral, or upper, surface of the sand dollar, these spines keep the sand out, while on the oral, or under, surface, they function together with the tube feet to allow the sand dollar to crawl slowly on the sand.
Food, such as seaweed and very small marine animal matter, is swept into the centrally located mouth by hairlike cilia on the spines. Many sand dollars also have elongated slitlike holes, or lunules, perforating the shell in a symmetrical arrangement. The function of these openings is not known.