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Posted by on Jan 9, 2016 in Tell Me Why |

What Is a Sand Dollar?

What Is a Sand Dollar?

Have you ever taken a walk along the beach to collect seashells and found a gray disk shaped like a silver dollar? If so, chances are you found the “shell” of a sea animal known as a sand dollar that had been washed up by the tide onto the beach.

Sand dollars — sometimes called sea cookies, snapper biscuits, sand cakes, cake urchins or pansy shells — are species of flat, burrowing echinoids that belong to the order Clypeasteroida.

Sand dollars are related to sea urchins, sea cucumbers and starfish. Sand dollars live on the sandy bottoms of coastal waters.

A living sand dollar’s body is covered with short, movable spines used for digging and crawling. When the sand dollar dies, the body tissues decay and the spines drop off, revealing the round, flat skeleton.

Gray spots form a star-shaped pattern on its back. Unlike the white color of dead sand dollars, live sand dollars are usually green, purple or blue. Some people think live sand dollars look like fuzzy cookies!

Live sand dollars are covered with a dense, velvety layer of short spines and tubular feet. They use these spines and tubular feet to burrow into the sand and move around.

Sand dollars crawl along the ocean floor with their mouths toward the ground, eating microscopic particles of food. Most sand dollars live 8-10 years. The age of any particular sand dollar can be determined by counting the growth rings on the plates of its hard skeleton.

Sand dollar skeletons feature a pattern that looks like a flower. This pattern is where sand dollar’s when alive, tubular feet are located. In addition to helping the sand dollar move, these tubular feet also help direct food found on the ocean floor to the sand dollar’s mouth.

Content for this question contributed by Alesia Keller, resident of Pittsburgh, Allegheny County, Commonwealth of Pennsylvania, USA