Sand Dollar, a small disc-shaped marine animal closely related to the sea urchin. Sand dollars live on the sandy ocean floor. Their grayish-white skeletal remains are often found washed up on coastal beaches.
Sand dollars are usually about 3 inches (7.5 cm) in diameter and 3/8 inch (1 cm) thick. Most sand dollars are purple or blue. They have a dense velvety covering of short spines and tiny muscular projections called tube feet. The spines and tube feet are used for locomotion and for burrowing into sand. Sand dollars creep about the ocean floor, mouth side down, feeding on minute organic particles.
Actually, a sand dollar can’t live on the beach. Most sand dollars live in shallow coastal waters. Sand dollars that people often find washed up on the shore are the skeletons of dead animals. There are no spines on a sand dollar skeleton. But a sand dollar does have spines when it is alive. And that’s why a sand dollar is an echinoderm.
A sand dollar is shaped like a big coin. It is about 2 to 4 inches (5 to 10 centimeters) wide. It’s flat, like a sea star. But like a sea urchin, it doesn’t have arms. On top of a sand dollar skeleton, you can see a pattern that looks like a flower. This is where some of a sand dollar’s tube feet are located. A sand dollar uses its tube feet to breathe. Oxygen from the water goes through the thin skin of the animal’s feet.
Live sand dollars look like fuzzy cookies. They are covered with many short spines. Besides the special tube feet on their tops, sand dollars also have tube feet on their undersides. They use these feet to get food and to crawl around.Both sand dollars and sea stars have their mouths on the undersides of their bodies. But sand dollars do not push their stomachs out or swallow animals with large shells. Instead, sand dollars sift through the sand and catch tiny organisms with their sticky tube feet. The tube feet pass the food along grooves that lead to the animal’s mouth.
Sand dollars are of the class Echinoidea of the phylum Echinodermata.