They are carnivores that feed on fish, shrimp, crabs and other cephalopods. A bite from a Blue-Ringed octopus, found in the South Pacific, is almost always fatal to humans. However, it takes a lot of provocation to get any octopus to bite a person. The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. Octopuses do not have shells at all, while squids have a small internal shell.
Cephalopods have a more developed nervous system than other mollusks.
They also have very well developed eyesight that is used in finding prey. Once prey is found, it is grasped firmly and eaten with a mouth located at the base of the arms. Cephalopods also have a parrot-like beak which is used in biting into prey. An octopus has eight arms. These extra two arms are called tentacles.