Cestoda
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| Cestoda | ||||||||||||
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 Scolex of Taenia solium
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Subclass Cestodaria: Subclass Eucestoda: |
Cestoda is a class of parasitic flatworms, commonly called tapeworms, that live in the digestive tract of vertebrates as adults and often in the bodies of various animals as juveniles. Taenia saginata, the beef tapeworm, can grow up to 40 feet long (12 m); other species may grow to over 100 feet (30 m).[1]
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[edit] Overview
Researchers describe the gut-dwelling worm as segmented and band-like in its adult stage.[2] Its first stage in tissues and organs of vertebrates, including humans, is the growth of a cyst-like juvenile (or metacestode).
[edit] Anatomy
[edit] Scolex
The worm's scolex ("head") attaches to the intestine of the definitive host. In some species, the scolex is dominated by bothria, which are sometimes called "sucking grooves", and function like suction cups. Other species have hooks and suckers that aid in attachment. Cyclophyllid cestodes can be identified by the presence of four suckers on their scolex. Tapeworms have sharp hooks on one side of the head. these dig into the host intestine lining.
While the scolex is often the most distinctive part of an adult tapeworm, it is often unnoticed in a clinical setting as it is inside the patient. Thus, identifying eggs and proglottids in feces is important.
[edit] Muscular system
The main nerve center of a cestode is in its scolex; as a cerebral ganglion. Motor and sensory innervation depends on the number and complexity of the scolex. Smaller nerves emanate from the commissures to supply the general body muscular and sensory ending. The cirrus and vagina are innervated and sensory endings around the genital pore are more plentiful than other areas. Sensory function includes both tactoreception and chemoreception. Some nerves are only temporary. These are in the proglottids, and stop working with a detach.
[edit] Proglottids
The body is composed of successive segments (proglottids). The sum of the proglottids is called a strobila, which is thin, resembling a strip of tape, and is the source of the common name "tapeworm". Like some other flatworms, cestodes use flame cells (protonephridia) for excretion, which are located in the proglottids.
Mature proglottids are released from the tapeworm's posterior end and leave the host in feces
Because each proglottid contains the male and female reproductive structures, they can reproduce independently. It has been suggested by some biologists that each should be considered a single organism, and that the tapeworm is actually a colony of proglottids.
The layout of proglottids comes in two forms, craspedote, meaning proglottids are overlapped by the previous proglottid, and acraspedote which indicates a non-overlapping conjoined proglottid.
[edit] Taxonomy
There are fourteen recognised orders of Cestodes: the Amphilinidea, Gyrocotylidea and 12 orders belonging to the Eucestoda. Within the Eucestoda the Spathebothriidea appear to be a sister group to the remaining 11 orders. [3] The Pseudophyllidea and Haplobothriidea appear to form a clade as do Cyclophyllidea, Nippotaeniidea and Tetrabothriidea.
[edit] See also
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Wikimedia Commons has media related to: Cestoda |
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Wikispecies has information related to: Cestoda |
- Diphyllobothrium (Fish tapeworm)
- Cysticercosis
- List of parasites (human)
- Tapeworm infection
[edit] Footnotes
- ^ "The Persistent Parasites". Time Magazine (Time Inc). 1957-04-08. http://www.time.com/time/magazine/article/0,9171,809356-1,00.html.
- ^ Philip Craig; Akira Ito (October 2007). "Intestinal Cestodes". Current Opinion in Infectious Diseases 20 (5): 524–532.
- ^ Olson P.D., Caira J.N. (1999) Evolution of the major lineages of tapeworms (Platyhelminthes: Cestoidea) inferred from 18S ribosomal DNA and elongation factor-1alpha. J. Parasitol. 85(6):1134-1159
[edit] References
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This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (February 2008) |
- Campbell, Reece, and Mitchell, Biology, 1999
- Merck Manual of Medication Information, Second Home Edition, Online Version, Tapeworm Infection 2005
- Mayo Clinic Website on infectious diseases, Mayo Clinic - Tapeworm Infection, 2006
- Medline Plus - Taeniasis (tapeworm infection)
- University of South Carolina - School of Medicine - CESTODES (TAPE WORMS)
This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.
[edit] External links
- How Disgusting are Tapeworms? Article from TalktotheVet.com
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