Sand dollars usually eat algae and organic matter found along the ocean floor, though some species will tip on their side to catch organic matter floating in ocean currents. Fine, hair-like cilia cover these tiny spines. The spines on the somewhat flattened topside and underside of the animal allow it to burrow or creep through the sediment when looking for shelter or food. The common sand dollar, Echinarachnius parma, can be found in the Northern Hemisphere from the intertidal zone to the depths of the ocean, while the keyhole sand dollars (three species of the genus Mellita) can be found on many a wide range of coasts in and around the Caribbean Sea. Sand dollars live in waters below the mean low water line, on or just beneath the surface of sandy and muddy areas. Sand dollars can be found in temperate and tropical zones along all continents. Spines on the underside of a sand dollar on the beach at Hilton Head Island, South Carolina 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 Caribbean sand dollar or inflated sea biscuit, Clypeaster rosaceus, is thicker in height than most. In South Africa, they are known as pansy shells from their suggestion of a five-petaled garden flower. Other names for the sand dollar include sand cakes, pansy shells, snapper biscuits, cake urchins, and sea cookies. Sand dollars are named as such not for their monetary value, but because of their appearance. To beachcombers of the past, this suggested a large, silver coin, such as the old Spanish dollar (diameter 38–40 mm). The test lacks its velvet-like skin of spines and has often been bleached white by sunlight. The term "sand dollar" derives from the appearance of the tests (skeletons) of dead individuals after being washed ashore. Live sea biscuit, Clypeaster rosaceus, commonly found off Key Biscayne, Florida family Monophorasteridae Lahille, 1896 †.family Mellitidae Stefanini, 1912 - Keyhole sand dollars.family Dendrasteridae Lambert, 1900 - Pacific eccentric sand dollar.family Echinarachniidae Lambert in Lambert & Thiéry, 1914.family Echinocyamidae Lambert & Thiéry, 1914.family Plesiolampadidae Lambert, 1905 †.family Fossulasteridae Philip & Foster, 1971 †.These result from the adaptation of sand dollars, in the course of their evolution, from creatures that originally lived their lives on top of the seabed ( epibenthos) to creatures that burrow beneath it ( endobenthos).Ĭlypeaster aegypticus, showing internal buttressesĪccording to World Register of Marine Species: The anus of sand dollars is located at the back rather than at the top as in most urchins, with many more bilateral features appearing in some species. Unlike other urchins, the bodies of sand dollars also display secondary front-to-back bilateral symmetry with no morphological distinguishing features between males and females. The mouth of the sand dollar is located on the bottom of its body at the center of the petal-like pattern. The pores are perforations in the endoskeleton through which podia for gas exchange project from the body. The petal-like pattern in sand dollars consists of five paired rows of pores. The bodies of adult sand dollars, like those of other echinoids, display radial symmetry. Dead individuals are commonly found with their empty test devoid of all surface material and bleached white by sunlight. Individuals which are very recently dead or dying (moribund) are sometimes found on beaches with much of the external morphology still intact. The velvety spines of live sand dollars appear in a variety of colors-green, blue, violet, or purple-depending on the species. Coordinated movements of the spines enable sand dollars to move across the seabed. In living individuals, the test is covered by a skin of velvet-textured spines which are covered with very small hairs ( cilia). The test of certain species of sand dollar have slits called lunules that can help the animal stay embedded in the sand to stop it from being swept away by an ocean wave. The test consists of calcium carbonate plates arranged in a fivefold symmetric pattern. As with all members of the order Clypeasteroida, they possess a rigid skeleton called a test. Sand dollars are small in size, averaging from three to four inches. Clypeaster rosaceus (aboral and oral faces) by Ernst Haeckel (1904)
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