ammonoid

ammonoid

[am-uh-noid]
noun
any cephalopod mollusk of the extinct order Ammonoidea, from the Devonian to the Cretaceous periods, having a coiled, chambered shell.

Origin:
1880–85; < Neo-Latin Ammonoidea, equivalent to Ammon(ites) name of the order + -oidea -oidea; see ammonite2

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Science Dictionary
ammonoid   (ām'ə-noid')  Pronunciation Key 
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.
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