Round worms in human large intestine, illustration - stock illustration

Round worms in human large intestine, computer illustration. Roundworms, or nematodes, include numerous free-living and pathogenic species. Pinworm (Enterobius vermicularis) and whipworm (Trichuris trichiura) usually settle in the large intestine, while ascarids (Ascaris lumbricoides) and hookworms (Ancylostoma duodenale and Necator americanus) invade the small intestine and extraintestinal locations.