A phylum of worms, having a long, round, and generally smooth body; the roundworms. They are mostly parasites, in plants and animals, but some are free-living in soil or water. Also called Nematoidea.
A division of the Articulata, having the body formed of numerous rings or annular segments, and without jointed legs. The principal subdivisions are the Chætopoda, including the Oligochæta or earthworms and Polychæta or marine worms; and the Hirudinea or leeches. See Chætopoda.
unsegmented worms: roundworms; threadworms; eelworms
segmented worms: earthworms; lugworms; leeches