Temporal range: 323.2 – 0 Ma Late Carboniferous – Recent
The octopus (// or //) is a cephalopod mollusc of the order Octopoda. It has two eyes and four pairs of arms and, like other cephalopods, it is bilaterally symmetric. It has a beak, with its mouth at the center point of the arms. It has no internal or external skeleton (although some species have a vestigial remnant of a shell inside their mantles), allowing it to squeeze through tight places. Octopuses are among the most intelligent and behaviorally diverse of all invertebrates.
Octopuses inhabit 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. They trail their eight arms behind them as they swim. All octopuses are venomous, but only one group, the blue-ringed octopuses, 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.
Octopuses appear in mythology as sea monsters like the Kraken of Norway and the Akkorokamui of the Ainu, and probably the Gorgon of ancient Greece also. A battle with an octopus appears in Victor Hugo's book Toilers of the Sea, inspiring other works such as Ian Fleming's Octopussy. Octopuses appear in Japanese erotic art, shunga. They are eaten in many parts of the world, especially the Mediterranean and the Asian seas.
- 1 Etymology and pluralization
- 2 Biology
- 3 Evolution
- 4 Relationship to humans
- 5 See also
- 6 References
- 7 External links
Etymology and pluralization
The scientific Latin term octopus was derived from Ancient Greek ὀκτώπους (oktōpous, "eight-footed"), a compound form of ὀκτώ (oktō, "eight") + πούς (pous, "foot"). Related to the word "octopus" are the terms "Octopoda" (the taxonomic order of cephalopod molluscs that comprises the octopuses) and the adjectival octopoid (with the suffix -oid, which signifies a resemblance to, but distinction from, something).
The standard pluralized form of "octopus" in the English language is "octopuses" //, although the Ancient Greek plural "octopodes" // ahk-TOP-oh-dees, has also been used historically. The alternative plural "octopi" – which misguidedly assumes it is a Latin " -us"-word – is considered grammatically incorrect. It is nevertheless used frequently enough to make it notable, and was formally acknowledged by the descriptivist Merriam-Webster 11th Collegiate Dictionary and Webster's New World College Dictionary. The Oxford English Dictionary (2008 Draft Revision) lists "octopuses", "octopi", and "octopodes", in that order, labeling "octopodes" as rare and noting that "octopi" is based on a misunderstanding. In contrast, New Oxford American Dictionary (3rd Edition 2010) lists "octopuses" as the only acceptable pluralization, with a usage note indicating "octopodes" as being still occasionally used but "octopi" as being incorrect.
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 limb are muscular hydrostats.
Octopuses can be divided into two suborders, the Incirrina (or Incirrata) and the Cirrina (or Cirrata). The incirrate octopuses are distinguished from the cirrate octopuses by their absence of "cirri" filaments (found with the suckers), as well as by the lack of paired swimming fins on the head. Unlike most other cephalopods, the majority of octopuses – those in the Incirrina – have almost entirely soft bodies with no internal skeleton. They lack a protective outer shell like the nautilus; the cuttlefish and squid retain an internal bony structure that is the remnant of an external shell, while the rest of the cephalopods retain only a small sliver of hard chitin at the rear of the mantle. The beak, similar in shape to a parrot's beak, is also made of chitin and is the only other 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, with some species living 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 live for only 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, the removal of both optic glands after spawning was found to result in the cessation of broodiness, the 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 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 molluscs, octopuses have gills that 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.
The 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. Despite this delegation of control, octopus arms do not become tangled or stuck to each other because the suction cups have chemical sensors that recognize octopus skin and prevent self-attachment. 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.
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.
Due to their intelligence, octopuses in some countries are on the list of experimental animals on which surgery may not be performed without anesthesia, a protection usually extended only to vertebrates. In the UK from 1993 to 2012, the common octopus (Octopus vulgaris) was the only invertebrate protected under the Animals (Scientific Procedures) Act 1986. In 2012, this legislation was extended to include all cephalopods in accordance with a general EU directive.
The octopus's primary defense is to hide or to disguise itself through camouflage and mimicry, though some species are venomous and have conspicuous warning coloration (aposematism). 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 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.
The 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, and leucophores (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 manner similar 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.
When octopuses reproduce, the male uses a specialized arm called a hectocotylus to transfer spermatophores (packets of sperm) from the terminal organ of the reproductive tract (the cephalopod "penis") into the female's mantle cavity. The hectocotylus in benthic octopuses is usually the third right arm. Males die within a few months of mating. 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 about 200,000 eggs (this figure dramatically varies between families, genera, species and also individuals).
Pacific striped octopuses share food and habitation but most other octopuses are solitary outside of mating.
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, called statocysts, 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 also have an excellent sense of touch. The octopus's suction cups are equipped with chemoreceptors so the octopus can taste what it is touching. The arms contain tension sensors so the octopus knows whether its arms are stretched out. However, it has a very poor proprioceptive sense. The tension receptors are not sufficient for the brain to determine the position of the octopus's body or arms. (It is not clear whether the octopus brain would be capable of processing the large amount of information that this would require; the flexibility of the octopus's arms is much greater than that of the limbs of vertebrates, which devote large areas of cerebral cortex to the processing of proprioceptive inputs.) As a result, the octopus does not possess stereognosis; that is, it does not form a mental image of the overall shape of the object it is handling. It can detect local texture variations, but cannot integrate the information into a larger picture.
The neurological autonomy of the arms means the octopus has great difficulty learning about the detailed effects of its motions. The brain may issue a high-level command to the arms, but the nerve cords in the arms execute the details. There is no neurological path for the brain to receive proprioceptive feedback about just how its command was executed by the arms; the only way it knows just what motions were made is by observing the arms visually, i.e. exteroception.
Octopuses might use the statocyst (a sac-like structure containing a mineralised mass and sensitive hairs) to register sound. The common octopus can hear sounds between 400 Hz and 1000 Hz, and hears best at a frequency of 600 Hz.
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 and Amphioctopus 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 octopus 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.
Bottom-dwelling octopuses eat mainly crabs, polychaete worms, and other molluscs such as whelks and clams. Open-ocean octopuses eat mainly prawns, fish and other cephalopods. They usually inject their prey with a paralysing saliva before dismembering it into small pieces with their beaks. Octopuses feed on shelled molluscs either by using force, or by drilling a hole in the shell, injecting a secretion into the hole, and then extracting the soft body of the mollusc.
The giant Pacific octopus, Enteroctopus dofleini, is often cited as the largest known 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 known 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).
Fossil history and phylogeny
Cephalopods have existed for around 500 million years, although octopus ancestors were in the Carboniferous seas around 300 million years ago. The oldest octopus fossil is Pohlsepia. The Coleoids appeared around the same time as the Ammonoids.
- Class Cephalopoda
- Subclass Nautiloidea: nautilus
- Subclass Coleoidea
- Superorder Decapodiformes: squid, cuttlefish
- Superorder Octopodiformes
- Family †Trachyteuthididae (incertae sedis)
- Order Vampyromorphida: vampire squid
- Order Octopoda
- Genus †Keuppia (incertae sedis)
- Genus †Palaeoctopus (incertae sedis)
- Genus †Paleocirroteuthis (incertae sedis)
- Genus †Pohlsepia (incertae sedis)
- Genus †Proteroctopus (incertae sedis)
- Genus †Styletoctopus (incertae sedis)
- Suborder Cirrina: finned deep-sea octopus
- Suborder Incirrina
- Superfamily Octopodoidea
- Superfamily Argonautoidea
Relationship to humans
Ancient peoples of the Mediterranean were aware of the octopus, as evidenced by certain artworks and designs of prehistory. For example, a stone carving found in the archaeological recovery from Bronze Age Minoan Crete at Knossos (1900 – 1100 BC) has a depiction of a fisherman carrying an octopus.
The octopus ... seeks its prey by so changing its colour as to render it like the colour of the stones adjacent to it; it does so also when alarmed.— Aristotle
Aristotle noted that the octopus had a hectocotyl arm and suggested it might be used in sexual reproduction. This claim was widely disbelieved until its rediscovery in the 19th century. It was described in 1829 by the French zoologist Georges Cuvier, who supposed it to be a parasitic worm, naming it as a new species, Hectocotylus octopodis. Other zoologists thought it a spermatophore; the German zoologist Heinrich Müller believed it was designed to detach during copulation. Finally in 1856 the Danish zoologist Japetus Steenstrup demonstrated that while it is used to transfer sperm, it only rarely detaches.
The Gorgon of Greek mythology has been thought to have been inspired by the octopus or squid, the octopus itself representing the severed head of Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes. The Kraken are legendary sea monsters of giant proportions said to dwell off the coasts of Norway and Greenland, usually portrayed in art as a giant octopus attacking ships. Linnaeus included it in the first edition of his 1735 Systema Naturae. 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 Akkorokamui is a gigantic octopus-like monster from Ainu folklore.
A battle with an octopus plays a significant role in Victor Hugo's book Travailleurs de la mer (Toilers of the Sea), relating to his time on the island of Guernsey. Ian Fleming's 1966 short story collection Octopussy and The Living Daylights, and the 1983 James Bond film were partly inspired by Hugo's book.
In John Steinbeck's novella Sweet Thursday, the marine biologist "Doc" is studying what the denizens of Cannery Row call " devilfish". Doc's study of octopuses to ascertain whether their behavior displays emotional responses similar to humans, such as apoplexy, is a major plot device in the novella. The former Beatle Ringo Starr wrote a 2014 children's book based on his 1969 song "Octopus's Garden". The book is illustrated by Ben Court.
In popular culture
In Pixar's 2016 film Finding Dory, a sequel to its highly successful 2003 Finding Nemo, Hank the octopus plays a major role in helping Dory find her parents. According to Pixar personnel, the character is based on a mimic octopus.
The biologist P. Z. Myers noted in his science-blog, Pharyngula, that octopuses appear in "extraordinary" graphic illustrations involving women, tentacles, and bare breasts. In Japan, erotic art, shunga, includes ukiyo-e woodblock prints such as Katsushika Hokusai's 1814 print Tako to ama (The Dream of the Fisherman's Wife), in which an ama diver is sexually intertwined with a large and a small octopus. The print is a forerunner of tentacle erotica.
Octopus is eaten in many cultures. They are a common food in Mediterranean and Asian sea areas. The arms and sometimes other body parts are prepared in various ways, often varying by species or geography.
Live octopuses are eaten in several countries around the world, including the US. Animal welfare groups have objected to this practice on the basis that octopuses can experience pain. In support of this, since September 2010, octopuses being used for scientific purposes in the EU are protected by EU Directive 2010/63/EU which states "...there is scientific evidence of their [cephalopods] ability to experience pain, suffering, distress and lasting harm. In the UK, this means that octopuses used for scientific purposes must be killed humanely, according to prescribed methods (known as "Schedule 1 methods of euthanasia").
Though octopuses can be difficult to keep in captivity, some people keep them as pets. They often escape even from supposedly secure tanks, due to their problem-solving skills, mobility and lack of rigid structure.
As a metaphor
Since it has numerous arms emanating from a common center, the octopus is often used as a metaphor for a powerful and manipulative organization, sometimes negatively.
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|The Wikibook Dichotomous Key has a page on the topic of: Octopoda|
- The Cephalopod Page
- TONMO.COM – The Octopus News Magazine Online
- Tree of Life website: information about cephalopods along with pictures and videos
- Discussion about the plural
- An octopus's shark encounter – footage of an octopus eating a shark (also in QuickTime format)
- Camouflage in action
- Video showing an Octopus escaping through a 1-inch (25 mm) hole
- Bipedal Octopuses- Video, Information, Original paper
- "Why Cephalopods Change Color" (PDF). (359 KB)
- Video of walking octopuses