The class Cephalopod means "head foot".  Squids, cuttlefish, nautiluses, and octopi are the members of this class.  All cephalopods posses a set of tentacles (arm like structures) surrounding their mouths.  The tentacles are used to capture pray.  They have a well-developed head with advanced eyes.

Among cephalopods only the nautilus posses an external shell.  All the members of this class are marine and carnivorous.  Cephalopods are famous for their speed and agility.