Baumiller, Tomasz K. Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan.
- Additional Reading
One of three Paleozoic subclasses of the Crinoidea consisting of over 350 genera ranging from the Ordovician to the Permian. Its members generally lack fixed brachials such that the arms are free above the level of the radials. The calyx may be monocyclic, consisting of a circlet of basal and a circlet of radial plates (illus. a), or dicyclic, having an additional circlet of infrabasal plates (illus. b). The arms, constructed of serially arranged brachials, may be simple or branched. Each arm plate may be bare or give rise to a slender, unbifurcated branchlet called a pinnule. Articulating surfaces of adjacent brachials may be smooth, forming a tight, inflexible suture, or each may possess a central ridge. In the latter case, abutting ridges of adjacent brachials form a mechanical fulcrum allowing a substantial degree of movement and flexibility. The anus may lie flush with the tegmen or be elevated on a tube of variable length and diameter.
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 10,000 highly qualified scientists and 45 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