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noun Echinoidea n. pl. (Written also Echinidea, and Echinoida) (Zoöl.) The class Echinodermata which includes the sea urchins. They have a calcareous shell, usually more or less spheroidal or disk-shaped, composed of many united plates, and covered with movable spines. See Spatangoid, Clypeastroid.
Collaborative International Dictionary of English 0.48
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