What is "cestoda"

Cestoda \Cestoda\ n. [NL., gr. Gr. kesto`s girdle + -oid.] (Zo["o]l.) A class of parasitic worms (Platelminthes) of which the tapeworms are the most common examples. The body is flattened, and usually but not always long, and composed of numerous joints or segments, each of which may contain a complete set of male and female reproductive organs. They have neither mouth nor intestine. See Tapeworm. [Written also Cestoidea.]

Syn: class Cestoda, Cestoidea.

Cestoidea \Ces*toid"e*a\ (s[e^]s*toid"[-e]*[.a]), n. pl. [NL., gr. Gr. kesto`s girdle + -oid.] (Zo["o]l.) same as cestoda; -- an older usage. [Written also Cestoda.]

Cestoda (Cestoidea) is a class of parasitic flatworms, of the phylum Platyhelminthes. Biologists informally refer to them as cestodes. The best-known species are commonly called tapeworms. All cestodes are parasitic and their life histories vary, but typically they live in the digestive tracts of vertebrates as adults, and often in the bodies of other species of animals as juveniles. Over a thousand species have been described, and all vertebrate species may be parasitised by at least one species of tapeworm.

Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork ( Taenia solium), beef ( T. saginata), and fish ( Diphyllobothrium spp.), or if they live in, or eat food prepared in, conditions of poor hygiene ( Hymenolepis or Echinococcus species).

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). Species using small vertebrates as hosts, though, tend to be small. For example, vole and lemming tapeworms are only in length, and those parasitizing shrews only .

Tapeworm parasites of vertebrates have a long history: recognizable clusters of cestode eggs, one with a developing larva, have been discovered in fossil feces ( coprolites) of a shark dating to the mid- to late Permian, some 270 million years ago.