Cestoda

Cestoda (Cestoidea) is the name given to a class of parasitic flatworms, commonly called tapeworms, of the phylum Platyhelminthes. Its members live in the digestive tract of vertebrates as adults, and often in the bodies of various animals as juveniles. Over a thousand species have been described, and all vertebrate species can be parasitised by at least one species of tapeworm. Several species parasitise humans after being consumed in underprepared meat such as pork (Taenia solium), beef (T. saginata), and fish (Diphyllobothrium spp.), or in food prepared in conditions of poor hygiene (Hymenolepis spp. or Echinococcus spp.).

T. saginata, the beef tapeworm, can grow up to 20 m (65 ft); the largest species, the whale tapeworm Polygonoporus giganticus, can grow to over 30 m (100 ft).