The common sand dollar is the skeleton or "test" of a marine animal. By the time the test washes up on the beach it is missing its velvety covering of minute spines and appears somewhat bleached from the sun.
Sand dollars are in the Echinoids class of marine animals. When alive, the local species, Echinarachnius parma is outfitted in a maroon-colored suit of moveable spines that encompass the entire shell. Like its close relative the sea urchin, the sand dollar has five sets of pores arranged petal pattern. The pores are used to move sea water into its internal water-vascular system which allows for movement.
Sand dollars live beyond mean low water on top of or just beneath the surface of sandy or muddy areas. The spines on the somewhat flattened underside of the animal allow it to burrow or to slowly creep through the sand. Fine, hair-like cilia cover the tiny spines. These cilia, in combination with a mucous coating, move food to the mouth opening which is in the center of the star shaped grooves on the underside of the animal. Its food consists of plankters and organic particles that end up in the sandy bottom.
On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference of soft bottom areas as well as convenience for reproduction. The sexes are separate and gametes are released into the water column as in most echinoids. The free-swimming larvae metamorphose through several stages before the test begins to form and they become bottom dwellers.
Sources:
External Links:
The Sand Dollar Legend - The history of the sand dollar and a legend about them.