Octopus

Blue-Ringed Octopus

The octopus is a cephalopod  of the order Octopoda. Octopuses have two eyes and four pairs of arms and like other cephalopods are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms. Most octopuses have no internal or external skeleton, allowing them to squeeze through tight places. Octopuses are highly intelligent, probably the most intelligent of all invertebrates.

The octopus inhabits many diverse regions of the ocean, especially coral reefs. For defense against predators, they hide, flee quickly, expel ink, or use color-changing camouflage. An octopus trails its eight arms behind it as it swims. All octopuses are venomous, but only the small blue-ringed octopuses are deadly to humans.



In the larger sense, there are around 300 recognized octopus species, which is over one-third of the total number of known cephalopod species. The term octopus may also be used to refer only to those creatures in the genus Octopus.

Octopuses are highly intelligent, likely more so 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. Their short lifespans limit the amount they can ultimately learn. There has been much speculation to the effect that almost all octopus behaviors are independently learned rather than instinct-based, although this remains largely unproven. They learn almost no behaviors from their parents, with whom young octopuses have very little contact.

Most octopuses can eject a thick blackish ink in a large cloud to aid in escaping from predators. The main colouring agent of the ink is melanin, which is the same chemical that gives humans their hair and skin colour. This ink cloud is thought to reduce the efficiency of olfactory organs, which would aid an octopus's evasion from predators that employ smell  for hunting, such as sharks. Ink clouds of some species might serve as pseudomorphs, or decoys that the predator attacks instead.

Octopuses move about by crawling or swimming. Their main means of slow travel is crawling, with some swimming. Jet propulsion is their fastest means of locomotion, followed by swimming and walking.