NematoideaNem`a*toi"de*a\, n. pl. [NL., fr. gr. ?, ?, thread + -oid.] (Zo["o]l.) An order of worms, having a long, round, and generally smooth body; the roundworms. they are mostly parasites. Called also Nematodea, and Nematoda. Note: The trichina, stomach worm, and pinworm of man belong to this group. See also Vinegar eel, under Vinegar, and Gapeworm.