Anderson, O. Roger Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York.
Harley, John P. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.
Last reviewed:August 2019
Show previous versions
- Related Primary Literature
- Additional Reading
A taxon of marine protozoans belonging to the Acantharea. Acanthometrida (also known as Arthracanthida) is a taxonomic grouping (sometimes considered as an order or subclass) placed within the Acantharea (Acantharia) taxon. All members are unicellular planktonic marine protozoa with axopodia (rigid, linear cellular projections). Long slender pseudopodia (temporary projections) are found in certain members as well. Mitochondria are always present and contain flattened cristae. No cilia are present in the trophic phase. Members have a skeleton, made up of strontium sulfate (celestite), that is limited to 20 radially arranged rods that extend from the center, forming a characteristic pattern in which angles are quite exact, as in Acanthometra (see illustration). Because strontium sulfate is soluble in seawater, no acantharean fossils exist. The central endoplasm contains numerous nuclei and other organelles. The cytoplasm surrounding the spines contains a conical array of contractile microfilaments (myophrisks or myonemes that are calcium-activated) containing the contractile protein actin. The microfilaments expand or contract the gelatinous sheath surrounding the cell, which allows for changes in the level of flotation. Electron microscopic research shows that the microfilaments are arranged in two sets of bands; one set runs parallel to the axis of the spine, and the other runs crosswise, thus producing a cross-fibrillar network. Cysts and flagellated swarmers represent two stages of the life cycle, which is not completely known at present. The endoplasm often contains zooxanthellae (small dinoflagellates living in the protozoan's endoplasm). See also: Acantharea; Celestite; Protozoa; Strontium
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