The class Cestoda consists of long, flat, ribbonlike worms that are commonly called tapeworms. Tapeworms are obligatory parasites, ones that cannot survive independent of a host, that live in the intestines of vertebrate hosts. They form an extremely varied group, and nearly every vertebrate species is associated with a different parasitic cestode. Most cestodes make use of one or more intermediate hosts to bring them into the body of the ultimate host. Some cestodes can achieve impressive lengths—worms of up to 15 meters (50 feet) have been observed.

Characteristics of Cestodes

All tapeworms share a body plan. At the front end is a head region called the scolex. The scolex maintains a hold on the host's digestive tract and has many suckers and hooks for this purpose. The scolex also contains the tape-worm's sense organs, which consist primarily of cells sensitive to touch and chemical stimuli, as well as...