Adult cestodes have long, flat bodies, which are made of segments called proglottids. Mature proglottids, which are located in the posterior part of the body, are released in the host's intestines. Each proglottid contains both male and female sexual organs and can self-generate eggs, which are expelled together with the host's feces. Although generally measuring about 10 to 16 feet, adult T. saginata can reach 82 feet in length and live up to five years.
Cestodes have an intermediate host before completing their life cycle in the digestive tract of the definitive host as adults. Taenia species that parasitize humans often use pigs or cattle as the intermediate hosts. When the animal eats egg-contaminated food, the dormant egg hatches, and the larvae passes from the digestive tract to the bloodstream, later accommodating in several organs and muscles. The larvae, or cysticerci, continue their life cycle when people eat contaminated meat. The larvae grow and become adults, while feeding on the nutrients found in the host's digestive system.
Scolex is the head of a cestode when in the larval or adult stage, and this head adapts to attach the animal to the host's intestine. Some species have tentacles in their scolex, which work like suction cups, while others have structures similar to hooks that help to keep the worm firmly attached to the host.
Cestodes lack some organs and systems that are common to other species of non-parasitic flatworms. As cestodes do not have a mouth or digestive system, they feed by absorbing the nutrients found in the host's digestive tract through skin. They also lack other specialized systems, such as the respiratory and the circulatory systems. Cestodes perform anaerobic respiration, which means they can live in environments without oxygen.