Cephalopods are molluscan animals that live in the sea. The group includes the modern octopi and squids as well as many fossil forms. The name cephalopod means "head foot" and it looks as though its feet (actually tentacles) are growing out of its head. The soft parts of the cephalopod animals are not fossilized, but the shell fossils are common in some strata. The inside of the fossil cephalopod shells are very similar to the internal parts of the modern Nautilus, a squid-like animal with a coiled shell. Because the shell structure is similar, we infer that the fossil cephalopods animals were similar to Nautilus when they were alive.
Cephalopods had a variety of shell shapes. Some were coiled and some were straight (orthocone).