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Sand dollars, like all members of the order Clypeasteroida, possess a rigid skeleton known as a test. The test consists of calcium carbonate plates arranged in a fivefold radial pattern. The common sand dollar, Echinarachnius parma, is widespread in ocean waters of the Northern Hemisphere, from the intertidal zone to considerable depths. It can be found in temperate and tropical zones. The keyhole sand dollar (three species, genus Mellita) is found on a wide range of coasts in and around the Caribbean Sea. Other English names for the creatures include sand cake and cake urchin. The Caribbean sand dollar or inflated sea biscuit, Clypeaster rosaceus, is thicker in height than most.¬¬¬ ¬In Spanish-speaking areas of the Americas, the sand dollar is most often known as galleta de mar (sea cookie); the translated term is often encountered in English. The various common terms (sand dollar, sea biscuit, etc.) sometimes appear printed in hyphenated forms (sand-dollar, sea-biscuit).