What is "echinoida"

Echinoidea \Ech`i*noi"de*a\, n. pl. [NL. See Echinus, and -oid.] (Zo["o]l.) 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. [Written also Echinidea, and Echinoida.] [1913 Webster] ||

Echinoida is an order of sea urchins in the class Echinoidea. They are distinguished from other sea urchins by simultaneously possessing both an un-sculpted test and a feeding lantern with large plates fused across the top of each pyramid.