Intelligence

Octopuses are highly intelligent, possibly 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 evidence of a memory system that can store both short- and long-term memory. It is not known precisely what contribution learning makes to adult octopus behavior. Young octopuses learn almost no behaviors from their parents, with whom they have very little contact.

An octopus has a highly complex nervous system, only part of which is localized in its brain. Two-thirds of an octopus's neurons are found in the nerve cords of its arms, which have limited functional autonomy. Octopus arms show a variety of complex reflex actions that persist even when they have no input from the brain. Unlike vertebrates, the complex motor skills of octopuses are not organized in their brain using an internal somatotopic map of its body, instead using a nonsomatotopic system unique to large-brained invertebrates. Some octopuses, such as the mimic octopus, will move their arms in ways that emulate the shape and movements of other sea creatures.

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. Octopuses often break out of their aquariums and sometimes into others in search of food. They have even boarded fishing boats and opened holds to eat crabs.

In some countries, octopuses are on the list of experimental animals on which surgery may not be performed without anesthesia. In the UK, until 2013, the common octopus, (Octopus vulgaris), was the only invertebrate protected under the Animals (Scientific Procedures) Act 1986 extending to them protections not normally afforded to invertebrates. In 2013, this legislation was extended to include all cephalopods.

Tool use


Amphioctopus marginatus travels with shells it has collected for protection
The octopus has been shown to use tools. At least four specimens of the veined octopus (Amphioctopus marginatus) have been witnessed retrieving discarded coconut shells, manipulating them, and then reassembling them to use as shelter.

Defense

An octopus's main (primary) defense is to hide, either not to be seen at all, or through camouflage and mimicry not to be detected as an octopus. Octopuses have several secondary defenses (defenses they use once they have been seen by a predator). The most common secondary defense is fast escape. Other defenses include distraction with the use of ink sacs and autotomising limbs.

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

An octopus's camouflage is aided by certain specialized skin cells which can change the apparent color, opacity, and reflectivity of the epidermis. Chromatophores contain yellow, orange, red, brown, or black pigments; most species have three of these colors, while some have two or four. Other color-changing cells are reflective iridophores, andleucophores (white). This color-changing ability can also be used to communicate with or warn other octopuses. The highly venomous blue-ringed octopus becomes bright yellow with blue rings when it is provoked. Octopuses can use muscles in the skin to change the texture of their mantle to achieve a greater camouflage. In some species, the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises. However in some species skin anatomy is limited to relatively patternless shades of one color, and limited skin texture. It is thought that octopuses that are day-active and/or live in complex habitats such as coral reefs have evolved more complex skin than their nocturnal and/or sand-dwelling relatives.

When under attack, some octopuses can perform arm autotomy, in a similar manner to the way skinks and other lizards detach their tails. The crawling arm serves as a distraction to would-be predators. Such severed arms remain sensitive to stimuli and move away from unpleasant sensations.

A few species, such as the mimic octopus, have a fourth defense mechanism. They 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.

Biology

Octopuses are characterized by their eight arms, usually bearing suction cups. The arms of octopuses are often distinguished from the pair of feeding tentacles found in squid and cuttlefish. Both types of limbs are muscular hydrostats. Unlike most other cephalopods, the majority of octopuses – those in the suborder most commonly known, Incirrina – 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 squid. The beak, similar in shape to a parrot's beak, and made of chitin, is the only hard part of their bodies. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from moray eels or other predatory fish. The octopuses in the less-familiar Cirrina suborder have two fins and an internal shell, generally reducing their ability to squeeze into small spaces. These cirrate species are often free-swimming and live in deep-water habitats, while incirrate octopus species are found in reefs and other shallower seafloor habitats.

Octopuses have a relatively short life expectancy, and some species live for as little as six months. Larger species, such as the giant pacific octopus, may live for up to five years under suitable circumstances. However, reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch. They neglect to eat during the (roughly) one-month period spent taking care of their unhatched eggs, eventually dying of starvation. In a scientific experiment, removal of both optic glands after spawning was found to result in cessation of broodiness, resumption of feeding, increased growth, and greatly extended lifespans.

Grimpoteuthis discoveryi, a finned octopus of the suborder Cirrina
Octopuses have three hearts. Two branchial hearts pump blood through each of the two gills, while the third is a systemic heart that pumps blood through the body. Octopus blood contains the copper-rich protein hemocyanin for transporting oxygen. Although less efficient under normal conditions than the iron-rich hemoglobin of vertebrates, in cold conditions with low oxygen pressure, hemocyanin oxygen transportation is more efficient than hemoglobin oxygen transportation. The hemocyanin is dissolved in the plasma instead of being carried within red blood cells, and gives the blood a bluish color. The octopus draws water into its mantle cavity, where it passes through its gills. As mollusks, their gills are finely divided and vascularized outgrowths of either the outer or the inner body surface.

The octopus

The octopus (/ˈɒktəpʊs/ or /ˈɒktəpəs/; plural: octopuses, octopi, or octopodes; see below) is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms and, like other cephalopods, they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms. Octopuses have no internal or external skeleton (although some species have a vestigial remnant of a shell inside their mantles), allowing them to squeeze through tight places. Octopuses are among the most intelligent and behaviorally flexible of all invertebrates.

The octopus inhabits many diverse regions of the ocean, including coral reefs, pelagic waters, and the ocean floor. They have numerous strategies for defending themselves against predators, including the expulsion of ink, the use of camouflage and deimatic displays, their ability to jet quickly through the water, and their ability to hide. An octopus trails its eight arms behind it as it swims. All octopuses are venomous, but only one group, the blue-ringed octopus, is known to be deadly to humans.

Around 300 species are recognized, which is over one-third of the total number of known cephalopod species. The term 'octopus' may also be used to refer specifically to the genus Octopus.