Ward, Peter D. Department of Geological Sciences, University of Washington, Seattle, Washington.
Teichert, Curt Department of Geological Sciences, University of Rochester, Rochester, New York.
Russell-Hunter, W. D. Department of Biology, Syracuse University, Syracuse, New York.
- Fossil record
- Description and behavior
- Links to Primary Literature
- Additional Readings
A group of externally shelled cephalopods, represented by the two living genera, Nautilus, known since the 1500s, and the more recently defined Allonautilus, which was seen alive for the first time only in 1986. Allonautilus differs from Nautilus not only in specific anatomical differences, but in the shell itself: unlike Nautilus, the shell of the living Allonautilus is covered with a thick blanket of periostracum (a thin membrane-like organic layer covering the outer shell surface), giving the shell a curious “bearded” appearance. The formal designation of this group as a subclass is now generally used only for those externally shelled cephalopods that resemble Nautilus in having completely coiled shells (thus the subclass includes Nautilus and Allonautilus). In living forms, the basic structural plan includes a shell consisting of a septate phragmocone, a living chamber, and a siphuncle. In fossil nautiloids, this simple pattern is modified in great variety with respect to shell form and size, structure and size of the siphuncle, and the large number of devices to counteract the buoyancy of the phragmocone. The shape of fossil nautiloids may deviate in many ways from the simple Nautilus model (Fig. 1); the length of straight or slightly curved shells varies from less than 2.5 cm (1 in.) to more than 10 m (33 ft). Few coiled shells are larger than Nautilus. Also, the siphuncle may vary considerably in size and shape (Fig. 1). The aperture of the living chamber may be constricted or contracted into various shapes, and the interiors of siphuncle and camerae may be partially filled by layers of aragonite and conchiolin. See also: Cephalopoda
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