Echinoidea, also known as sea urchins and sand dollars, are small spiny, globular animals. There are about 950 species that inhabit the oceans, all the way from the intertidal zone to 5,000 meters deep. Their shell, or "test," is round and usually three to ten centimeters across. Common colors include black and dull shades of green, olive, brown, purple, blue, and red, Sea urchins move slowly, mostly feeding on algae. These creatures also have five-fold symmetry and move by mean by hundreds of tiny, transparent, adhesive "tube feet."
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Sand dollars are extremely flattened, burrowing sea urchins. In living individuals their skeleton is covered by a skin of velvet-textured spines, which are covered with very small hairs, also known as cilia. Coordinated movements of the spines enable these organisms to move across the seabed. They can appear in multiple colors including green, blue, violet, or purple.
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