| Helminth worms attack the digestive tract and other internal organs of the vertebrate body and cause a wide variety of parasitic diseases. These worms include such diverse forms as the roundworms (nematodes), flukes (trematodes), tapeworms (cestodes), thorny-headed worms (acanthocephalans), and tongue worms (linguatulids). Many species are only able to complete their life cycle by spending time in a variety of animal hosts. |