Moore, Donald V. Department of Microbiology, Southwestern Medical School, University of Texas, Dallas, Texas.
Last reviewed:April 2019
Show previous versions
- Reproductive system
- Nervous system
- Excretory system
- Links to Primary Literature
- Additional Readings
A distinct phylum of helminths (parasitic worms), commonly known as the spiny- or thorny-headed worms. The phylum Acanthocephala comprises three classes: Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala (a suggested fourth class, Polyacanthocephala, has been determined to be part of Eoacanthocephala). The adult members (Fig. 1) of the phylum—termed acanthocephalans, spiny-headed worms, or thorny-headed worms—are parasitic in the alimentary canal of vertebrates. All acanthocephalans are obligatory parasites throughout their entire life cycle; no known member exists as a free-living organism. Approximately 1100 species have been described from all classes of vertebrates, although more species occur in fish (but not elasmobranch fish) than in birds and mammals and only a relatively few species are found in amphibians and reptiles. The geographical distribution of acanthocephalans is worldwide, but genera and species do not have a uniform distribution because some species are confined to limited geographic areas. Host specificity is well established in some species, whereas others exhibit a wide range of host tolerance. The same species never occurs normally, as an adult, in cold-blooded and warm-blooded definitive hosts. The fact that larval development occurs in arthropods gives support to the postulation that the ancestors of acanthocephalans were parasites of primitive arthropods during or before the Cambrian Period and became parasites of vertebrates as this group arose and utilized arthropods for food. Molecular analyses have indicated a close relationship with rotifers (microscopic, mainly free-living aquatic animals), and some researchers have suggested that acanthocephalans and rotifers should be combined into a single taxonomic group (Syndermata). See also: Archiacanthocephala; Arthropoda; Eoacanthocephala; Invertebrate phylogeny; Medical parasitology; Palaeacanthocephala; Parasitology; Rotifera; Vertebrata
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information