A Roundworm or Nematode has a "tube" like body within a tube, with a fluid- filled cavity in between the tubes.
Most nematodes are parasites, such as ascarids, filarids, pinworms, hookworms, and...
Round worms cause many harmful disease trichinosis. Baylisascaris are deadly to humans. There are many types of round worms which can be deadly and dangerous to human beings.