Is a nautilus a cephalopod a gastropod or a bivalve?

A nautilus is a cephalopod. It belongs to the class Cephalopoda, which also includes octopuses, squids, and cuttlefish. Unlike gastropods (snails and slugs) and bivalves (clams and oysters), cephalopods are characterized by their highly developed nervous systems and ability to exhibit complex behaviors. The nautilus is unique among living cephalopods for its coiled, chambered shell.