‖n. pl. [ NL., fr. radiatus, p. p. See Radiate. ] (Zool.) An extensive artificial group of invertebrates, having all the parts arranged radially around the vertical axis of the body, and the various organs repeated symmetrically in each ray or spheromere. [ 1913 Webster ]

☞ It includes the cœlenterates and the echinoderms. Formerly, the group was supposed to be a natural one, and was considered one of the grand divisions of the animal kingdom. [ 1913 Webster ]