Common Sand Dollar | Sand, Dollar, Dollars, Skeletons, Spines

Common Sand Dollar

Common Sand Dollar (Echinarachnius parma) It is always a rare treat to find an intact sand dollar washed up on the beach. The whitish, round, hard discs that we see on shore are actually just the outer skeletons of the once living sand dollar animal. If you look closely at a sand dollar, you might see many tiny holes

covering the skeleton. When the sand dollar was alive, it was covered by many small, dark, reddish spines that stuck out from these holes and gave them an almost fuzzy appearance. On the top of the skeleton you might also notice that there is a petal pattern that looks similar to a five armed starfish. Sand dollars are, in fact, related to starfish but lack the long, protruding arms. A full grown sand dollar is about 3 inches in diameter. Female and male sand dollars look the same and are only distinguishable by their reproductive organs. The spines covering the sand dollars allow them to move around the sea floor and to burrow into the sand: a feat that is usually completed in less than ten minutes. Sand dollars search through the sand for organic material to eat, but they will also eat algae and plankton floating in the water. When a sand dollar comes upon food, it uses cilia, hair-like fibers lining the spines, to transport food to its mouth that is located on the underside of the sand dollar. With spines, hard outer skeletons and small bodies that provide little sustenance, sand dollars have few predators. However, some species of fish and sea stars can penetrate their defenses and prey upon them.

Sand dollars prefer to live in the intertidal zone in areas with soft sandy bottoms, where it is not unusual to find a large group of sand dollars gathered together. Not only are sand dollars found at the beach, but also in scientific laboratories. The eggs of the sand dollar are used in scientific research: specifically, to study cell division. Understanding the process of cell division in sand dollar eggs can teach us more about the development and proliferation of cancer in humans.

Both live sand dollars and their skeletons are safe to handle, but the skeletons are fragile and easily broken, so handle with care. Sand dollar skeletons that wash up on shore are usually bleached by the sun so appear bright white and are easy to spot. If you are interested in finding some pristine sand dollars, the best time to go looking is after a storm when the skeletons will be deposited on shore.

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