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Eucestoda
Eucestoda is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria. The Eucestoda are commonly referred to as tapeworms. Larvae are hexacanth, having six posterior hooks on the scolex (head), in contrast to the decacanth (ten-hooked) Cestodaria. All species of the Eucestoda are endoparasites of vertebrates, living in the digestive tract or related ducts. Examples are the pork tapeworm (''Taenia solium'', with a human definitive host and pigs as the secondary host) and ''Moniezia expansa'', the definitive hosts of which are ruminants).
==Body Structure==
Adult Eucestoda have a white-opaque dorso-ventrally flattened appearance, and are elongated, ranging from 1 mm to 25 m in length. Almost all members, except members of the orders Caryophyllidea and Spathebothriidea, are polyzoic with repeated sets of reproductive organs down the body length, and almost all members, except members of the order Dioecocestidae, are protandral hermaphrodites. Most except caryophyllideans consist of a few to 4000 proglottids (segments) that show a characteristic body differentiation pattern into scolex (head), neck, and strobila.〔Mehlhorn, Heinz. "Eucestoda Classification." Encyclopedia of Parasitology. 2008. p. 495-497〕
The scolex, located at the anterior end, is a small (usually less than 1 mm) holdfast organ with specific systems for fastening itself to materials: rostrum, acetabula, suckers, bothria, grooves, and hooks. The small neck region, directly behind the scolex, consists of an undifferentiated tissue region of proglottid proliferation, leading into a zone of increasing and continuous proglottid differentiation. As such, the main and largest section of the body, the strobila, consists of a chain of increasingly mature proglottids. These cytological processes are not well understood at present.
Members of the Eucestoda have no mouth or digestive tract, and instead absorb nutrients through a layer of microtriches over the tegument at the shared body wall surface.〔Rohde, Klaus. "Eucestoda." AccessScience. McGraw-Hill Ryerson〕 In addition to the body wall, several other systems are common to the whole length of the tapeworm, including excretory canals, nerve fibers, and longitudinal muscles.〔"Encyclopedia of Parasitology"〕 The excretory system is responsible for osmoregulation and consists of blind-ending flame bulbs communicating through a duct system. The nervous system, often referred to as a "ladder system," is a system of longitudinal connectives and transverse ring commissures.〔"AccessScience"〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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