ˌ ̷ ̷ ̷ ̷ˈȯidēə noun plural
Usage: capitalized
Etymology: New Latin, from Nautilus + -oidea
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