Category:Echinoidea

Ech`i*noi"de*a, n. pl. Etym: [NL. See Echinus, and -oid.] (Zoöl.)

Defn: The class Echinodermata which includes the sea urchins. They have a calcareous, usually more or less spheroidal or disk-shaped, composed of many united plates, and covered with movable spines. See Spatangoid, Clypeastroid. [Written also Echinidea, and Echinoida.]