ChaetopodaCh[ae]*top"o*da\, n. pl. [NL., from Gr. ? hair + -poda.] (Zo["o]l.) A very extensive order of Annelida, characterized by the presence of lateral set[ae], or spines, on most or all of the segments. They are divided into two principal groups: Oligoch[ae]ta, including the earthworms and allied forms, and Polych[ae]ta, including most of the marine species.