Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites).
In Walking with... SeriesEditOphthalmosaurus tried to eat one, but couldn't bite through its shell. (In the book it was identified as Perisphinctes).
This first half of this episode featured Cameroceras, the largest carnivore of the Ordovician period. It had no suckers, but ridges on its powerful tentacles with which it crushed its prey.
Cameroceras appeared in a cameo in this episode (as an Orthocone).