‖n. pl. [ NL., from Gr. &unr_; hair + -poda. ] (Zool.) A very extensive order of Annelida (segmented worms), characterized by the presence of lateral setæ, or spines, on most or all of the segments. They are divided into two principal groups: Oligochæta, including the earthworms and allied forms, and Polychæta, including most of the marine species. [ 1913 Webster ]