American E-Store: Octopus ..Eight Legs .. Thousands Eggs.

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.

Octopuses have two eyes and four pairs of arms and, like other hydrocephalus, they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms.

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 decimate 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 only to those creatures in the genus Octopus.

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 internalskeleton. 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.

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 bloodcontains 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.

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's main (primary) defense is to hide, either not to be seen at all, or throughcamouflage 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.
Octopuses have keen eyesight. Like other cephalopods, they can distinguish the polarization of light. Color vision appears to vary from species to species, being present in O. aegina but absent in O. vulgaris.

Attached to the brain are two special organs, calledstatocysts, that allow the octopus to sense the orientation of its body relative to horizontal. An autonomic response keeps the octopus's eyes oriented so the pupil slit is always horizontal.

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.

They crawl by walking on their arms, usually on many at once, on both solid and soft surfaces, while supported in water. In 2005, some octopuses (Adopus aculeatus andAmphioctopus marginatus under current taxonomy) were found to walk on two arms, while at the same time resembling plant matter.

This form of locomotion allows these octopuses to move quickly away from a potential predator while possibly not triggering that predator's search image for octopus (food). A study of this behavior conducted by the Weymouth Sea Life Centre led to the suggestion that the two rearmost appendages may be more accurately termed 'legs' rather than 'arms'. Some species of octopuses can crawl out of the water for a short period, which they may do between tide pools while hunting crustaceans or gastropods or to escape predators.
Octopuses swim by expelling a jet of water from a contractile mantle, and aiming it via a muscular siphon.

The giant Pacific octopus, Enteroctopus dofleini, is often cited as the largest octopus species. Adults usually weigh around 15 kg (33 lb), with an arm span of up to 4.3 m (14 ft). The largest specimen of this species to be scientifically documented was an animal with a live mass of 71 kg (156.5 lb). The alternative contender is the seven-arm octopus, Haliphron atlanticus, based on a 61 kg (134 lb) carcass estimated to have a live mass of 75 kg (165 lb). However, a number of questionable size records would suggest E. Dofleini is the largest of all octopus species by a considerable margin; one such record is of a specimen weighing 272 kg (600 lb) and having an arm span of 9 m (30 ft).