Nematodes or nematodes are also known as "roundworms" or "cylindrical worms" due to the shape of their body in cross section. They are not segmented.
They have a digestive tube, with a mouth and anus.
They are predominantly aquatic, but also thrive in moist terrestrial environments.
Some nematodes are free-living, but many are parasitic, such as roundworms, whipworm, and filariae. They feed on the blood or other fluids of the host.
They reproduce by both parthenogenesis and sexual reproduction. The females deposit the eggs in the host and leave with the feces, from where they pass to other animals through the digestive tract.
The whipworm, roundworms, or anisakis are examples of nematodes.
By Anilocra [Public domain], via Wikimedia Commons