Cretaceous. The cephalopods are considered to be the most highly advanced of the molluscs. All are marine, and the foot is modified to form a series of tentacles and a head. In some the shell is external, but in the most familiar cephalopods the shell is internal or absent.
The University of Toledo
Digital Initiatives, University of Toledo Libraries
environmental sciences; virtual exhibitions
"Phylum Mollusca, Class Cephalopoda" (2017). Rock and Mineral Exhibit. 105.