An octopus is a mollusk within the class cephalopod that inhabits many diverse regions of the ocean, especially coral reefs. There are over 300 recognized octopus species
It has eight flexible arms, which trail behind it as it swims. Most octopuses have no internal or external skeleton, allowing them to squeeze through tight places. An octopus has a hard beak, with its mouth at the center point of the arms. Octopuses have three hearts. Two pump blood through each of the two gills, while the third pumps blood through the body. For defense against predators, they hide, flee quickly, expel ink, or use color changing camouflage. Octopuses are bilaterally symmetrical, like other cephalopods, with two eyes and four pairs of arms. They are not radially symmetrical, like sea stars.
Octopuses are highly intelligent, probably more intelligent than any other order of invertebrates. Maze and problem solving experiments have shown that they do have both short and long term memory. Their short 6 month lifespans limit the amount they can ultimately learn. They learn almost no behaviors from their parents, with whom young octopuses have very little contact.
In laboratory experiments, octopuses can be readily trained to distinguish between different shapes and patterns. They have been reported to practice observational learning, although the validity of these findings is widely contested on a number of grounds. Octopuses have also been observed in what some have described as play, repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them. They often break out of their aquariums and sometimes into others in search of food. They have boarded fishing boats and opened holds to eat crabs.
Most octopuses can eject a thick blackish ink in a large cloud to aid in escaping from predators. The ink cloud is thought to dull smell, which is particularly useful for evading predators that are dependent on smell for hunting, such as sharks. Ink clouds of some species might serve as pseudomorphs, or decoys that the predator attacks instead.
An octopus’ camouflage is aided by certain specialized skin cells which can change the apparent color, opacity, and reflectiveness of the epidermis. This color changing ability can also be used to communicate with or warn other octopuses. Octopuses can use muscles in the skin to change the texture of their mantle in order to achieve a greater camouflage. In some species the mantle can take on the spiky appearance of seaweed, or the bumpy texture of a rock. A few species, such as the Mimic Octopus, have a fourth defense mechanism and can combine their highly flexible bodies with their color changing ability to accurately mimic other, more dangerous animals such as lionfish, sea snakes, and eels.
Though octopuses can be difficult to keep in captivity, some people keep them as pets. Octopuses often escape even from supposedly secure tanks due to their problem solving skills, mobility and lack of rigid structure. Octopuses are also quite strong for their size. Octopuses kept as pets have been known to open the covers of their aquariums and survive for a time in the air in order to get to a nearby feeder tank and gorge themselves on the fish there. They have also been known to catch and kill some species of sharks.
The Hawaiian creation myth relates that the present cosmos is only the last of a series, having arisen in stages from the wreck of the previous universe. In this account, the octopus is the lone survivor of the previous, alien universe. The Moche people of ancient Peru worshipped the sea and its animals and octopuses were often depicted in their art. A stone carving found in the archaeological recovery from Bronze Age Minoan Crete at Knossos has a depiction of an octopus.