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The octopus is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. The term may also refer to only those creatures in the genus Octopus. In the larger sense, there are 289 different octopus species, which is over one-third the total number of cephalopod species.


 


Octopuses are characterized by their eight arms (not tentacles), usually bearing suction cups. These arms are a type of muscular hydrostat. Unlike most other cephalopods, the majority of octopuses 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. 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.


Long arms, short lives: Octopuses have a relatively short life span, and some species live for as little as six months. Larger species, such as the North Pacific Giant 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, for they neglect to eat during the (roughly) one month period spent taking care of their unhatched eggs.

Three hearts! Octopuses have three hearts. Two pump blood through each of the two gills, while the third pumps blood through the body. Octopus blood contains the copper-rich protein hemocyanin for transporting oxygen. Less efficient than the iron-rich hemoglobin of vertebrates, the hemocyanin is dissolved in the plasma instead of being bound in red blood cells and gives the blood a blue color. Octopuses draw water into their mantle cavity where it passes through its gills. As a mollusc, octopus gills are finely divided and vascularilzed outgrowths of either the outer or the inner body surface.

Three defense strategy: Three defensive mechanisms are typical of octopuses: ink sacs, camouflage, and autotomising limbs. Most octopuses can eject a thick blackish ink in a large cloud to aid in escaping from predators. They also have specialized skin cells both for color changing and light reflection and refraction. They use this ability to blend into the environment to hide, communicate with other octopuses, or warn. The very poisonous Blue-ringed Octopus becomes bright yellow with blue rings when it is provoked. When under attack, some octopuses can autotomise their limbs, in a similar manner to skinks and other lizards. The crawling arm serves as a distraction to would-be predators; this ability is also used in mating. 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 and eels.

As smart as a cat: Octopuses are highly intelligent, probably the most intelligent of any of the invertebrates, with their intelligence supposedly comparable to that of the average housecat. Maze and problem-solving experiments show that they have both short- and long-term memory, although their short lifespans limit the amount they can ultimately learn.

Arm nerves: 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 a remarkable amount of autonomy. Octopus arms show a wide variety of complex reflex actions arising on at least three different levels of the nervous system. Some octopuses, such as the mimic octopus, will move their arms in ways that emulate the movements of other sea creatures.

Slow travel - crawl, Fast travel - Swim: Octopuses move about by crawling or swimming. Their main means of slow travel is crawling, with some swimming. Their only means of fast travel is swimming. Their fastest movements can be up to eighty five miles per hour. They can go extremely fast due to the fact that their three hearts have to pump through each vascular pump at a paralell sequence. They go this fast if hungry or if in danger.

Pretend to be a coconut: They crawl by walking on their arms, usually on many at once, on solid surfaces, while supported in water. In 2005 it was reported that some octopuses can walk on two arms on a solid surface, while at the same time imitating a coconut or a clump of seaweed.

They swim by expelling a jet of water from a contractile mantle, and aiming it via a muscular siphon.


When octopuses reproduce, males use a specialized arm called a hectocotylus to insert spermatophores (packets of sperm) into the female's mantle cavity. The hectocotylus is usually the third right arm. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature. After they have been fertilized, the female lays roughly 200,000 eggs (this figure dramatically varies between families, genera, species and also individuals).

The female hangs these eggs in strings from the ceiling of her lair, or individually attatched to the substratum depending on the species. After the eggs hatch, the young larval octopuses must spend a period of time drifting in clouds of plankton, where they feed on copepods, larval crabs and larval seastars until they are ready to sink down to the bottom of the ocean, where the cycle repeats itself. In some deeper dwelling species, the young do not go through this period. This is a dangerous time for the larval octopuses; as they become part of the plankton cloud they are vulnerable to many plankton eaters

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 Kingdom: Animalia

 Phylum: Mollusca

 Class: Cephalopoda

 Subclass: Coleoidea

 Superorder: Octopodiformes

 Order: Octopoda