Schaeffer, Bobb American Museum of Natural History, New York, New York.
Last reviewed:August 2015
Show previous versions
- Evolutionary development
- Modern features
- Related Primary Literature
- Additional Reading
The subclass within the Chondrichthyes (cartilaginous fishes) that includes the sharks (Selachii) and the skates and rays (Batoidea). According to traditional classifications, the Chondrichthyes is divided into two subclasses: the Elasmobranchii (sharks, skates, and rays) and the Holocephali (chimaeras or ratfishes). It is probable that both groups arose independently during the Silurian or Early Devonian from a group of extinct armored fishes, the Placodermi. Members of the Elasmobranchii (elasmobranchs) are distinguished by separate gill openings, amphistylic or hyostylic jaw suspension, and sensory organs (ampullae of Lorenzini) in the head region. Characters shared with the holocephalans include a variably calcified cartilaginous endoskeleton, placoid scales, a urea retention mechanism, clasper organs in the male for internal fertilization, and the absence of an air (swim) bladder. See also: Batoidea; Chimaeriformes; Chondrichthyes; Copulatory organ; Placodermi; Scale (zoology); Selachii; Swim bladder
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