‖n. pl. [ NL., fr. echiurus, the name of one genus (Gr. 'e`chis an adder + o'yra` tail) + -oid. ] (Zoöl.) A division of Annelida which includes the genus Echiurus and allies. They are often classed among the Gephyrea, and called the armed Gephyreans. [ 1913 Webster ]