Nematodes are the second most diverse animal phylum (after the arthropods). Free-living nematodes are abundant in soils and sediments, where they feed on bacteria and detritus. Some nematodes are plant parasites, including organisms that cause disease in economically important crops. Others parasitize animals (including humans). Well-known parasitic nematodes include hookworms, pinworms, Guinea worm (genus Dracunculus), and intestinal roundworms (genus Ascaris).