Unsegmented worms with elongated rounded body pointed at both ends; mostly free-living but some are parasitic; SYN. roundworm.
Unsegmented worm of the phylum Nematoda. Nematodes are pointed at both ends, with a tough, smooth outer skin. They include many free-living species found in soil and water, including the sea, but a large number are parasites, such as the roundworms and pinworms that live in humans, or the eelworms that attack plant roots. They differ from flatworms in that they have two openings to the gut (a mouth and an anus).