The octopus is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs.
Octopuses are characterized by their eight arms (not tentacles), usually bearing suction cups.
Unlike most other cephalopods, the majority of octopuses - those in the suborder most commonly known, Incirrata - have almost entirely soft bodies with no internal skeleton.
They have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or squids.
A beak, similar in shape to a parrot's beak, is their only hard part.
This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from morays or other predatory fish.
Octopuses are highly intelligent, probably more intelligent than any other order of invertebrates.
The exact extent of their intelligence and learning capability is much debated among biologists, but maze and problem-solving experiments have shown that they do have both short- and long-term memory.