: any of the class Cestoda of flatworms that are parasitic as adults in the alimentary tract of vertebrates including humans and as larvae in a great variety of vertebrates and invertebrates, that typically consist of an attachment organ usually with suckers, grooves, hooks, or other devices for adhering to the host's intestine followed by an undifferentiated growth region from which buds off a chain of segments of which the anterior members are little more than blocks of tissue, the median members have fully developed organs of both sexes, and the posterior members are degenerated to egg-filled sacs, that have no digestive system and absorb food through the body wall, and that have a nervous system consisting of ganglia and commissures in the scolex and longitudinal cords extending the length of the strobila—called also cestode; see beef tapeworm, cat tapeworm, dog tapeworm, fish tapeworm, fringed tapeworm, pork tapeworm
Any of about 3,000 species (class Cestoda, phylum Platyhelminthes) of bilaterally symmetrical parasitic flatworms 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. If these are ingested by an animal (the intermediate host) grazing on food contaminated with feces, they develop into larvae, which bore through the intestinal wall into the circulatory system and are carried to muscle tissues, which they burrow into, forming a dormant cyst. When meat is inadequately cooked, humans become infested with the larvae, which attach to the intestinal wall. 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 can also acquire tapeworms through fecal contamination of soil or water.