ammonoid

[ am-uh-noid ]
/ ˈæm əˌnɔɪd /

noun

any cephalopod mollusk of the extinct order Ammonoidea, from the Devonian to the Cretaceous periods, having a coiled, chambered shell.

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Origin of ammonoid

1880–85; <New Latin Ammonoidea, equivalent to Ammon(ites) name of the order + -oidea-oidea; see ammonite2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Scientific definitions for ammonoid

ammonoid
[ ămə-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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.