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ammonoid

[am-uh-noid] /ˈæm əˌnɔɪd/
noun
1.
any cephalopod mollusk of the extinct order Ammonoidea, from the Devonian to the Cretaceous periods, having a coiled, chambered shell.
Origin
1880-1885
1880-85; < Neo-Latin Ammonoidea, equivalent to Ammon(ites) name of the order + -oidea -oidea; see ammonite2
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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ammonoid in Science
ammonoid
  (ām'ə-noid')   
Any of various extinct cephalopods of the subclass Ammonoidea living from the Devonian to the Cretaceous Periods. Ammonoids had a symmetrical, coiled, chambered shell with angular sutures between the chambers. They are closely related to the nautiloids, including the modern-day chambered nautilus.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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