Any of about 3,000 species (class Cestoda, phylum Platyhelminthes) of bilaterally symmetrical parasitic flatworm s found worldwide.
Tapeworms range from 0.04 in. (1 mm) to more than 50 ft (15 m) long. The head bears suckers and often hooks for attaching to the liver or digestive tract of the host. Once attached, a tapeworm absorbs food through its body wall. The body is often divided into a head or scolex possessing the suckers and hooks, an unsegmented neck, and a series of proglottids (units containing both male and female reproductive organs) that continually form in a growth region at the base of the neck. Following fertilization, each mature proglottid containing thousands of embryos breaks off and is eliminated in the host's feces. The life cycle may require more than one host but otherwise somewhat resembles that of the roundworm trichina . Many species that infest humans belong to the genus Taenia ; the intermediate host is implied by the name (e.g., beef tapeworm, T. saginata ). Humans usually acquire tapeworms through fecal contamination of soil or water or inadequate cooking of meat or fish.