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The common name for a creature in the echinoderm phylum, order Clypeasteroida. Sand dollars are flat and round, and up to 16 cm (about 6 inches) in diameter. The outer shell is centered with a design which looks like a flower with five petals. When alive, the creature is covered with tiny brown spines that give it a velvety appearance. If taken from the water, the spines of the sand dollar are lost leaving calcitic circular shells which are often collected. The sand dollar is a bottom dweller which feeds on detritus particles found between sand grains.