Definition of Nautiloidea
1 : an order or other subdivision of Tetrabranchia comprising cephalopods having an external chambered shell that is either straight (as in Orthoceras) or variously curved or coiled and being important in the Ordovician and especially the Silurian but now represented only by the genus Nautilus
2 in some classifications : a subclass or other subdivision of Cephalopoda that is coextensive with Tetrabranchia
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Origin and Etymology of nautiloidea
New Latin, from Nautilus + -oidea
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