how big are nematodes?
<answer> Parasitic nematodes vary in length from several millimetres to approximately 2 metres and have larval stages and adult worms of both sexes. <context> See also: Roundworms written for patients. Nematodes (roundworms) have elongated, bilaterally long cylindrical bodies which contain an intestinal system and a large body cavity. Parasitic nematodes vary in length from several millimetres to approximately 2 metres and have larval stages and adult worms of both sexes. Approximately 60 species of roundworms are parasites of humans.