Ech`i*noi"de*a (?), n. pl. [NL. See Echinus, and -oid.] Zool.
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
© Webster 1913.