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Ammonoidea

A Dictionary of Earth Sciences | 1999 | | Copyright

Ammonoidea (ammonoids; phylum Mollusca, class Cephalopoda) Subclass of cephalopods which generally have planispirally coiled, septate shells (see SEPTUM). Characteristically the shells are tightly coiled and planispiral, although some are coiled loosely or spirally; the protoconch is globular; the shells may be either involute or evolute. Some forms have marked ventral keels; ribs and nodes may also be present. The siphuncle is variable but mainly ventral in position. Sutures are often very complex. Camaral deposits are absent. The Ammonoidea were probably tetrabranchiate (four-gilled) cephalopods. They constitute the largest cephalopod subclass, with 163 families including the ammonites, in which the suture lines form very complex patterns; the ceratites, in which part of the suture line is frilled; and the goniatites, with relatively simple suture lines. They range in age from Devonian to Upper Cretaceous. All members are now extinct. See also APERTURE; APTYCHUS; FORAMEN; PHRAGMOCONE; and VENTER.

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AILSA ALLABY and MICHAEL ALLABY. "Ammonoidea." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

AILSA ALLABY and MICHAEL ALLABY. "Ammonoidea." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-Ammonoidea.html

AILSA ALLABY and MICHAEL ALLABY. "Ammonoidea." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-Ammonoidea.html

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Ammonoidea

A Dictionary of Zoology | 1999 | | Copyright

Ammonoidea (phylum Mollusca, class Cephalopoda) A subclass of cephalopods which generally have planispirally, tightly coiled, septate shells (although some are coiled loosely or spirally). The protoconch is globular; the shells may be either involute or evolute. Some forms have marked ventral keels; ribs and nodes may also be present. The siphuncle is variable but mainly ventral in position. Sutures are often very complex. Cameral deposits are absent. The Ammonoidea were probably tetrabranchiate cephalopods. They constitute the largest cephalopod subclass, with 163 families, including the ammonites, in which the suture lines form very complex patterns; the ceratites, in which part of the suture line is frilled; and the goniatites, which have relatively simple suture lines. They range in age from Devonian to Upper Cretaceous. All members are now extinct.

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MICHAEL ALLABY. "Ammonoidea." A Dictionary of Zoology. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

MICHAEL ALLABY. "Ammonoidea." A Dictionary of Zoology. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O8-Ammonoidea.html

MICHAEL ALLABY. "Ammonoidea." A Dictionary of Zoology. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-Ammonoidea.html

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ammonoids

A Dictionary of Earth Sciences | 1999 | | Copyright

ammonoids See AMMONOIDEA.

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AILSA ALLABY and MICHAEL ALLABY. "ammonoids." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

AILSA ALLABY and MICHAEL ALLABY. "ammonoids." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-ammonoids.html

AILSA ALLABY and MICHAEL ALLABY. "ammonoids." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-ammonoids.html

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ammonoids

A Dictionary of Zoology | 1999 | | Copyright

ammonoids See AMMONOIDEA.

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MICHAEL ALLABY. "ammonoids." A Dictionary of Zoology. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

MICHAEL ALLABY. "ammonoids." A Dictionary of Zoology. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O8-ammonoids.html

MICHAEL ALLABY. "ammonoids." A Dictionary of Zoology. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-ammonoids.html

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