page_title: Cestoda
section_title: Proglottids
hierarchical_section_title: Cestoda / Anatomy / Proglottids
caption_attribution_description: ID#: 5261 Description: This micrograph reveals the organ morphology within Taenia solium tapeworm proglottids. The number of primary lateral uterine branches, i.e. the dark India ink stained irregularities, allows differentiation between the two species: T. saginata has 15-20 branches on each side, while Taenia solium has 7-13. Content Providers(s): CDC Creation Date: 1986 Copyright Restrictions: None - This image is in the public domain and thus free of any copyright restrictions. As a matter of courtesy we request that the content provider be credited and notified in any public or private usage of this image.
context_page_description: Cestoda is a class of parasitic worms in the flatworm phylum. Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of many similar units, known as proglottids, which are essentially packages of eggs which are regularly shed into the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish parasites.
  All cestodes are parasitic; many have complex life histories, including a stage in a definitive host in which the adults grow and reproduce, often for years, and one or two intermediate stages in which the larvae develop in other hosts. Typically the adults live in the digestive tracts of vertebrates, while the larvae often live in the bodies of other animals, either vertebrates or invertebrates. For example, Diphyllobothrium has at least two intermediate hosts, a crustacean and then one or more freshwater fish; its definitive host is a mammal. Some cestodes are host-specific, while others are parasites of a wide variety of hosts. Some six thousand species have been described; probably all vertebrates can host at least one species.
context_section_description: Once anchored to the host's intestinal wall, tapeworms absorb nutrients through their surface as their food flows past them. Cestodes are unable to synthesise lipids, which they use for reproduction, and are therefore entirely dependent on their hosts.
  The tapeworm body is composed of a series of segments called proglottids. These are produced from the neck by mitotic growth, which is followed by transverse constriction. The segments become larger and more mature as they are displaced backwards by newer segments. Each proglottid contains an independent reproductive tract, and like some other flatworms, cestodes excrete waste through flame cells (protonephridia) located in the proglottids. The sum of the proglottids is called a strobila, which is thin and resembles a strip of tape; from this is derived the common name "tapeworm". Proglottids are continually being produced by the neck region of the scolex, as long as the scolex is attached and alive.
  Mature proglottids are essentially bags of eggs, each of which is infective to the proper intermediate host. They are released and leave the host in feces, or migrate outwards as independent motile proglottids. The number of proglottids forming the tapeworm ranges from three to four thousand. Their layout comes in two forms: craspedote, meaning any given proglottid is overlapped by the previous proglottid, or acraspedote, indicating the proglottids do not overlap.
caption: Two proglottids of Taenia solium. This species has 7 to 13 branches of the uterus on each side (above and below in this micrograph).
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