Octopuses inhabit variousocean habitats, includingcoral reefs,pelagic waters, and theseabed; some live in theintertidal zone and others atabyssal depths. Most species grow quickly, mature early, and are short-lived. In most species, the male uses a specially-adapted arm to deliver sperm directly into the female's mantle cavity, after which he becomessenescent and dies, while the female deposits fertilised eggs in a den and cares for them until they hatch, after which she also dies. They are predators and huntcrustaceans,bivalves,gastropods and fish. Strategies to defend themselves against their own predators include expellingink,camouflage, andthreat displays, the ability to jet quickly through the water and hide, and deceit. All octopuses arevenomous, but only theblue-ringed octopuses are known to be deadly to humans.
The standardpluralised form ofoctopus in English isoctopuses;[8] the Ancient Greek pluralὀκτώποδες,octopodes (/ɒkˈtɒpədiːz/), has also been used historically.[9] The alternative pluraloctopi is usually considered etymologically incorrect because itwrongly assumes thatoctopus is a Latinsecond-declension-us noun or adjective when, in either Greek or Latin, it is athird-declension noun.[10][11] Historically, the first plural to commonly appear in English language sources, in the early 19th century, is the Latinate formoctopi,[12] followed by the English formoctopuses in the latter half of the same century. The Hellenic plural is roughly contemporary in usage, although it is also the rarest.[13]
Fowler's Modern English Usage states that the only acceptable plural in English isoctopuses, thatoctopi is misconceived, andoctopodespedantic;[14][15][16] the last is nonetheless used frequently enough to be acknowledged by thedescriptivistMerriam-Webster 11th Collegiate Dictionary andWebster's New World College Dictionary. TheOxford English Dictionary listsoctopuses,octopi, andoctopodes, in that order, reflecting frequency of use, callingoctopodes rare and noting thatoctopi is based on a misunderstanding.[17] TheNew Oxford American Dictionary (3rd Edition, 2010) listsoctopuses as the only acceptable pluralisation, and indicates thatoctopodes is occasionally used, but thatoctopi is incorrect.[18]
Thegiant Pacific octopus (Enteroctopus dofleini) is often cited as the largest octopus species. Adults usually weigh 10–50 kg (22–110 lb), with an arm span of up to 4.8 m (16 ft).[19] The largest specimen of this species to be scientifically documented reached a live mass of 71 kg (157 lb).[20] Much larger sizes have been claimed:[21] one specimen was recorded as 272 kg (600 lb) with an arm span of 9 m (30 ft).[22] A carcass of theseven-arm octopus,Haliphron atlanticus, weighed 61 kg (134 lb) and was estimated to have had a live mass of 75 kg (165 lb).[23][24] The smallest species isOctopus wolfi, which is around 2.5 cm (1 in) and weighs less than 1 g (0.035 oz).[25]
External characteristics
The octopus has an elongated body that isbilaterally symmetrical along its dorso-ventral (back to belly) axis; the head andfoot are on the ventral side, but act as the anterior (front). The head contains both the mouth and the brain.[26]: 343–344 The mouth has a sharpchitinousbeak and is surrounded by and underneath the foot, which evolved into flexible, prehensilecephalopod limbs, known as "arms", which are attached to each other near their base by a webbed structure.[26]: 343–344 [27]: 40–41 [28]: 13–15 The arms can be described based on side and sequence position (such as L1, R1, L2, R2) and divide into four pairs.[29]: 12 The two rear appendages are generally used to walk on the sea floor, while the other six are used to forage for food.[30] The bulbous and hollowmantle is fused to the back of the head and contains most of the vital organs.[28]: 13–15 [27]: 40–41 The mantle also has a cavity with muscular walls and a pair of gills; it is connected to the exterior by a funnel orsiphon.[26]: 343–344 [31]
Diagram of octopus from side, with gills, funnel, eye,ocellus (eyespot), web, arms, suckers,hectocotylus andligula labelled.
The skin consists of a thinepidermis with mucous cells and sensory cells and a fibrousdermis made ofcollagen and containing various cells that allow colour change.[26]: 362 Most of the body is made of soft tissue, allowing it to squeeze through tiny gaps; even the larger species can pass through a gap little more than 2.5 cm (1 in) in diameter.[27]: 40–41 Lacking skeletal support, the arms work asmuscular hydrostats and feature longitudinal, transverse, and circular muscles around a central axial nerve. They can squash and stretch, coil at any place in any direction or stiffen.[32][33]
The interior surfaces of the arms are covered with circular, adhesive suckers. The suckers allow the octopus to secure itself in place or to handle objects. Each sucker is typically circular and bowl-like and has two distinct parts: an outer disc-shapedinfundibulum and an inner cup-likeacetabulum, both of which are thick muscles covered inconnective tissue. Achitinous cuticle lines the outer surface. When a sucker attaches to a surface, the orifice between the two structures is sealed and the infundibulum flattens. Muscle contractions allow for attachment and detachment.[34][35][32] Each of the eight arms senses and responds to light, allowing the octopus to control its limbs even if its head is obscured.[36]
A finnedGrimpoteuthis species with its atypical octopus body plan
The cranium has twocartilaginous capsules each containing one large eye, which resembles those of fish. Thecornea is formed from atranslucent epidermal layer; the slit-shapedpupil forms a hole in theiris just behind the cornea. The lens hangs behind the pupil; photoreceptiveretinal cells line the back. The pupil can expand and contract; a retinal pigment screens incident light in bright conditions.[26]: 360–361
Some species differ in form from the typical body shape.Basal species, theCirrina, have gelatinous bodies with twofins located above the eyes, aninternal shell and mostly webbed arms that are lined with fleshy papillae orcirri underneath.[37][38]
Circulatory system
Octopuses have a closedcirculatory system, in which the blood remains inside blood vessels. They have three hearts; a systemic or main heart that circulates blood around the body and two branchial or gill hearts that pump it through the two gills. The systemic heart becomes inactive when the animal is swimming. Thus, the octopus loses energy quickly and mostly crawls.[29]: 19–20, 31–35 [27]: 42–43 Octopus blood contains thecopper-rich proteinhaemocyanin to transport oxygen. This makes the bloodviscous and it requires great pressure to pump it around the body;blood pressures can surpass 75 mmHg (10 kPa).[29]: 31–35 [27]: 42–43 [39] In cold conditions with low oxygen levels, haemocyanin transports oxygen more efficiently thanhaemoglobin.[40] The haemocyanin is dissolved in theblood plasma instead of carried within blood cells and gives the blood a bluish colour.[29]: 31–35 [27]: 42–43 [28]: 22
The systemic heart has muscular contractile walls and consists of a singleventricle and twoatria, which attach it to each of the two gills. The blood vessels consist of arteries, capillaries and veins and are lined with a cellularendothelium unlike that of most otherinvertebrates. The blood circulates through theaorta and capillary system, to thevenae cavae, after which the blood is pumped through the gills by the branchial hearts and back to the main heart. Much of the venous system is contractile, which helps circulate the blood.[26]: 358
Respiration
Octopus with open siphon. The siphon is used for respiration, waste disposal and discharging ink.
Respiration involves drawing water into the mantle cavity through an aperture, passing it through the gills, and expelling it through the siphon. Ingress is achieved by contraction of radial muscles in the mantle wall, and flapper valves shut when strong, circular muscles expel the water through the siphon.[41] Extensive connective tissue lattices support the respiratory muscles and allow them to inflate the respiratory chamber.[29]: 24–26 Thelamella structure of the gills allows for high oxygen uptake, up to 65% in water at 20 °C (68 °F).[42] Respiration can also play a role in locomotion, as an octopus can propel its body shooting water out of the siphon.[29]: 18 [39]
The thin skin absorbs additional oxygen. When resting, around 41% of oxygen absorption is through the skin, reduced to 33% when the octopus swims, despite the amount of oxygen absorption increasing as water flows over the body. When it is resting after a meal, skin absorption can drop to 3%.[43]
Digestion and excretion
The digestive system begins with thebuccal mass which consists of the mouth with the beak, thepharynx,radula and salivary glands.[29]: 71–74 The radula is serrated and made ofchitin.[27]: 40–41 Food is broken down and is forced into theesophagus by two lateral extensions of the esophageal side walls in addition to the radula. From there it is transferred to thegastrointestinal tract, which is mostly suspended from the roof of the mantle cavity. The tract consists of acrop, where the food is stored; a stomach, where it is mixed with other gut material; acaecum where the food is separated into particles and liquids and which absorbs fats; thedigestive gland, where liver cells break down and absorb the fluid and become "brown bodies"; and the intestine, where the built-up waste is turned into faecal ropes by secretions and ejected out of the funnel via therectum.[29]: 75–79
Duringosmoregulation, fluid is added to thepericardia of the branchial hearts. The octopus has twonephridia (equivalent to vertebrate kidneys) that are associated with the branchial hearts; these and their associated ducts connect the pericardial cavities with the mantle cavity. Each branch of thevena cava has renal appendages that pass over the thin-walled nephridium before reaching the branchial heart. Urine is created in the pericardial cavity, and is altered by excretion, of mostly ammonia, and absorption from the renal appendages, as it is passed along the associated duct and through the nephridiopore into the mantle cavity.[26]: 358–359
Acommon octopus (Octopus vulgaris) moving around. Its nervous system allows the arms to move with some autonomy.
Nervous system and senses
Octopuses and their relatives have a more expansive and complexnervous system than other invertebrates, containing over 500 millionneurons, around the same as a dog.[44][45][46] One part is localised in the brain, contained in a cartilaginous capsule. Two-thirds of the neurons are in the nerve cords of its arms. This allows their arms to perform actions with a degree of independence.[47] Learning mainly occurs in the brain, while arms make decisions independently when supplied with information.[48] A severed arm can still move and respond to stimuli.[49] Unlike in many other animals, including other mollusks, the movement of octopuses and their relatives are not organised in their brains via internalsomatotopic maps of their bodies.[50] Octopuses have the samejumping genes that are active in the human brain, implying anevolutionary convergence at molecular level.[51]
Like other cephalopods, octopuses have camera-like eyes.[44]Colour vision appears to vary from species to species, for example, it is present inA. aegina but absent inO. vulgaris.[52]Opsins in the skin respond to different wavelengths of light and help the animals choose a colouration that matches the surroundings and camouflages them;chromatophores in the skin can respond to light independently of the eyes.[53][54] An alternative hypothesis is thatcephalopod eyes in species that only have a singlephotoreceptor protein may usechromatic aberration to turn monochromatic vision into colour vision, though this lowers image quality. This would explain pupils shaped like the letter "U", the letter "W", or adumbbell, as well as the need for colourful mating displays.[55]
Attached to the optic capsules are two organs calledstatocysts (sac-like structures containing a mineralised mass and sensitive hairs), that allow the octopus to sense the orientation of its body, relative to both gravity and time (angular acceleration). Anautonomic response keeps the octopus's eyes oriented so that the pupil is always horizontal.[26]: 360–361 Octopuses may also use the statocyst to hear. The common octopus can hear sounds between 400 Hz and 1000 Hz, and hears best at 600 Hz.[56]
Octopuses have an excellentsomatosensory system. Their suction cups are equipped withchemoreceptors so they cantaste what they touch.[57] Octopus arms move easily because the sensors recognise octopus skin and prevent self-attachment.[58] Octopuses appear to have poorproprioceptive sense and must see their arms to keep track of their position.[59][60]
Ink sac
Theink sac is located under the digestive gland. A gland attached to the sac produces theink, and the sac holds it. The sac is close enough to the funnel for the octopus to shoot out the ink with a water jet. As the animal begins to shoot, the ink passes through glands which mix it with mucus and it leaves the funnel as a thick, dark blob which helps the animal to escape from a predator.[28]: 107 The mainpigment in the ink ismelanin, which gives it its black colour.[61] Cirrate octopuses usually lack the ink sac.[37]
Octopuseshave two sexes and have only one gonad (testis in males andovary in females) located posteriorly. The gonad depositsgametes into an adjacent cavity called the gonocoel. Agonoduct bridges the gonocoel with themantle cavity.[26]: 363–365 Anoptic gland creates hormones that cause the octopus to mature and age and stimulate gamete production. The timing of reproduction and lifespan depends on environmental conditions such as temperature, light and nutrition, which trigger the gland.[28]: 147 [62] The male has a specialised arm called ahectocotylus which it uses to transferspermatophores (packets of sperm) into the female's mantle cavity.[26]: 363–365 The hectocotylus inOctopus is usually the R3 arm, which has a spoon-shaped depression and a suckerless tip.[29]: 12–14 [26]: 363–365 Fertilisation may occur in the mantle cavity or in the surrounding water.[26]: 363–365
Reproduction has been studied in some species. In thegiant Pacific octopus, courtship includes changes in skin texture and colour, mostly in the male. The male may cling to the top or side of the female or position himself beside her. There is some speculation that he may first use his hectocotylus to remove any spermatophore or sperm already present in the female. He picks up a spermatophore from his spermatophoric sac with the hectocotylus, inserts it into the female's mantle cavity, and deposits it in the correct location in the opening of the oviduct. Two spermatophores are transferred in this way; these are about one metre (yard) long, and the empty ends may protrude from the female's mantle.[63] A complex hydraulic mechanism releases the sperm from the spermatophore.[26]: 363–365
Female giant Pacific octopus guarding strings of eggs
The eggs have large yolks;cleavage (division) is relatively shallow and agerminal disc develops at the pole. Duringgastrulation, the disc surrounds the yolk, forming a yolk sac, which eventually forms part of the gut. The embryo forms as the dorsal side of the disc grows upward, with a shell gland, gills, mantle and eyes on its dorsal side. The arms and funnel form on the ventral side of the disc, with the former moving upward to surround the mouth. The embryo consumes the yolk during development.[26]: 363–365
Over a month after mating, Giant Pacific octopuses lay eggs. The species can lay 180,000 eggs in a single clutch, whileO. rubescens clutches host up to 45,000 eggs whileO. vulgaris clutches can include 500,000 eggs.[64]: 75 Fertilised octopus eggs are laid as strings within a shelter.[63][28]: 26 Female giant Pacific octopuses nurture and protect their eggs for five months (160 days) until they hatch.[63] In colder waters, such as those offAlaska, it may take up to ten months for the eggs to completely develop.[64]: 74 In theargonaut (paper nautilus), the female is much larger than the male. She secretes a thin shell shaped like acornucopia, in which the eggs are deposited and in which she also resides and broods the young while swimming.[28]: 26, 141
Octopuses have short lifespans, living up to four years.[28]: 17 The lifecycles of some species finish in less than half a year.[27]: 152 For most octopuses, the ultimate life stage issenescence. It is the breakdown of cellular function without repair or replacement. It may last from weeks to a few months at most. Males senesce after maturity, while for females, it comes after they lay an egg clutch. During senescence, an octopus does not feed, quickly weakens, and becomes sluggish. Lesions begin to form and the octopus literally degenerates. They may die of starvation or get picked off by predators.[66] Senescence is triggered by the optic glands and experimental removal of them after spawning was found to extend their lifecycle and activity.[67]
Thecirrate species are often free-swimming and live in deep-water habitats.[38] Although several species live atbathyal andabyssal depths, only a single indisputable record documents their presence in thehadal zone; a species ofGrimpoteuthis (dumbo octopus) photographed at 6,957 m (22,825 ft).[69]
Behaviour and ecology
Octopuses are mostly solitary[28]: 17, 134 though a few are known to live in groups and interact regularly, usually in the context ofdominance and reproductive competition. This is likely the result of abundant food supplies combined with fewer den sites.[70] TheLarger Pacific striped octopus has been described as particularly social, living in groups of up to 40.[71][72] Octopuses hide in dens, which are typically crevices in rocky or other hard structures, including man-made ones. Small species may use abandoned shells and bottles.[28]: 69, 74–75 They cannavigate to a den without having to retrace their outward route.[73] They are not migratory.[27]: 45–46
Octopuses bring captured prey to the den to eat. Dens are often surrounded by amidden of dead and uneaten food items. These middens may attract scavengers such as fish, molluscs, andechinoderms.[74] On rare occasions, octopuseshunt cooperatively with other species, with fish as their partners. They regulate thespecies composition of the huntinggroup—and the behavior of theirpartners—by punching them.[75]
Octopuses typically locate prey by feeling through their environment;[28]: 60 some species hide and ambush their target.[76]: 54 When prey tries to escape, the octopus jets after it.[28]: 61 Octopuses may drill into the shells of crustaceans, bivalves and gastropods. It used to be thought that drilling was done by the radula, but it has now been shown that minute teeth at the tip of the salivary papilla are involved, and an enzyme in the toxic saliva is used to dissolve the calcium carbonate of the shell. This can take hours and once the shell is penetrated, the prey dies almost instantaneously. With crabs, tough-shelled species are more likely to be drilled, and soft-shelled crabs are torn apart.[78]
Some species have other modes of feeding.Grimpoteuthis either lacks or has a small radula and swallows prey whole.[37] In the deep-sea genusStauroteuthis, the suckers in most species have been altered intophotophores which are believed to fool prey by directing them to the mouth, making them one of the fewbioluminescent octopuses.[79]
Locomotion
Octopuses swim with their arms trailing behind.
Octopuses mainly move about by relatively slow crawling with some swimming in a head-first position.Jet propulsion or backward swimming, is their fastest means of locomotion, while crawling is slowest.[80] While crawling, the suckers adhere and detach from the substrate as the animal hauls itself forward with its powerful arm muscles.[32][80] In 2005,Adopus aculeatus and veined octopus (Amphioctopus marginatus) were found to walk on two arms, while at the same time mimicking plant matter.[81] This form of locomotion allows these octopuses to move quickly away from a potential predator without being recognised.[80] Some species of octopus can crawl out of the water briefly, which they may do between tide pools.[82][28]: 183 "Stilt walking" is used by the veined octopus when carrying stacked coconut shells. The octopus carries the shells underneath it with two arms, and progresses with an awkward gait supported by its remaining arms, which are stiffened.[83]
Most octopuses swim by expelling a jet of water from the mantle through the siphon into the sea. The direction of travel depends on the orientation of the siphon. When swimming, the head is at the front and the siphon is pointed backward but, when jetting, the visceral hump leads, the siphon points at the head and the arms trail behind, with the animal presenting afusiform appearance. In an alternative method of swimming, some species flatten themselves dorso-ventrally, and swim with the arms splayed; this may provide lift and be faster than normal swimming. Jetting is used to escape from danger, but is physiologically inefficient, requiring a mantle pressure so high as to stop the heart from beating, resulting in a progressive oxygen deficit.[80]
Cirrate octopuses cannot produce jet propulsion and swim using their fins. Their neutrally buoyant bodies float along while the fins are spread. They can also contract their arms and surrounding web to make sudden moves known as "take-offs". Another form of locomotion is "pumping", which involves symmetrical contractions of muscles in their webs producingperistaltic waves, moving them slowly.[37]
Octopuses are highlyintelligent.[84]Maze andproblem-solving experiments have shown evidence of a memory system that can store bothshort- andlong-term memory.[85] In laboratory experiments, octopuses can readily be trained to distinguish between different shapes and patterns. They have been reported to practiseobservational learning,[86] although the validity of these findings is contested.[84] Theveined octopus collects discardedcoconut shells, then uses them to build a shelter, an example oftool use.[83] Octopuses have also been observed in what has been described asplay: including moving around a bottle by jetting water at it.[87] Octopuses often break out of aquariums and sometimes into others in search of food.[82][88][89] Evidence indicates that octopuses havesentience and can feelpain.[90]
Camouflage and colour change
Video ofOctopus cyanea moving and changing its colour, shape, and texture
Octopuses usecamouflage to hunt and to avoid predators. To do this, they use specialised skin cells that change colour.Chromatophores contain yellow, orange, red, brown, or black pigments; most species have three of these colours, while some have two or four. Other colour-changing cells are reflective iridophores and white leucophores.[91] This colour-changing ability is also used to communicate with or warn other octopuses.[28]: 90–97 The energy cost of the complete activation of the chromatophore system is high, nearly matching the energy used at rest.[92]
Octopuses can create distracting patterns with waves of dark colouration across the body, a display known as the "passing cloud". Muscles in the skin change the texture of the mantle to achieve greater camouflage. In some species, the mantle can take on the bumpy appearance of algae-covered rocks. Diurnal, shallow water octopuses have more complex skin than their nocturnal and deep-sea counterparts. In the latter species, skin anatomy is limited to one colour or pattern.[28]: 89–97
Octopus' "moving rock" trick involves mimicking a rock and then inching across the open space with a speed matching that of the surrounding water.[93]
Aside from humans, octopuses are prey for fishes,seabirds,sea otters,pinnipeds,cetaceans, and other cephalopods.[94] Octopuses typically hide or disguise themselves by camouflage andmimicry; some have conspicuouswarning coloration (aposematism) ordeimatic behaviour ("bluffing" a threatening appearance).[28]: 90–97 An octopus may hide in their dens for as much as 40% of the day. When the octopus is approached, it may reach out an arm to investigate. 66% ofE. dofleini in one study had scars, with 50% missing arms.[94] The blue rings of the venomous blue-ringed octopus are hidden in muscular skin folds which contract when the animal is threatened, revealing the iridescent warning.[95] TheAtlantic white-spotted octopus (Callistoctopus macropus) becomes redder with bright white spots in adeimatic display. Displays are often reinforced by stretching out the animal's arms, fins or web to make it look as big and threatening as possible.[76]: 80–81
Octopus try to escape from a predator by ejecting an ink cloud, which acts as a "smoke-screen" or adecoy, as well as to interfere with the attacker's sense of smell.[96] When severed by a predator, some octopuses candetach their arm,[76]: 86–87 which cangrow back.[28]: 85 Some octopuses, such as themimic octopus, can combine their flexible bodies with their colour-changing ability to mimic other, more dangerous animals, such aslionfish, sea snakes, andeels.[97][98]
Pathogens and parasites
Cephalopods are known to be the intermediate or finalhosts of various parasiticcestodes,nematodes and copepods; 150 species ofprotistan andmetazoan parasites are recognised.[99] TheDicyemidae are a family of tiny worms found in the renal appendages of many species;[100] it is unclear whether they are parasitic orendosymbionts.Coccidians in the genusAggregata living in the gut cause serious illness in the host. Octopuses have aninnate immune system; theirhaemocytes locate the foreign invader and attack it viaphagocytosis, encapsulation, infiltration, orcytotoxicity. The haemocytes also contribute to healing injures.[101] A gram-negative bacterium,Vibrio lentus, can cause skin lesions, exposure of muscle and sometimes death.[102]
The scientific name Octopoda was first given as the order of octopuses in 1818 by English biologistWilliam Elford Leach,[103] who classified them as Octopoida the previous year.[2] Octopoda consists of around 300 known species[28]: 145 and were historically divided into two suborders, theIncirrina and the Cirrina.[104] More recent evidence suggests cirrates are the most basal species, not a uniqueclade.[105] The incirrate octopuses (the majority of species) lack the cirri and paired swimming fins of the cirrates.[38] In addition, the internal shell of incirrates is either present as a pair ofstylets or absent altogether.[106]
The Cephalopoda descended from a mollusc resembling theMonoplacophora in theCambrian some 530 million years ago. The Coleoidea, which brought their shells inside the body, diverged from thenautiloids in theDevonian some 416 million years ago. Around 276 million years ago, during thePermian, the coleoids split into two groups, theVampyropoda and theDecabrachia.[108] The octopuses arose from theMuensterelloidea within the Vampyropoda in theJurassic. The earliest octopus likely lived near the sea floor (benthic todemersal) in shallow marine environments.[108][109][107] Octopuses consist mostly of soft tissue, and so fossils are relatively rare. As soft-bodied cephalopods, they lack the external shell of most molluscs, including other cephalopods like the nautiloids and the (extinct)Ammonoidea.[110] They have eight limbs like otherColeoidea, but lack the extra specialised feeding appendages known astentacles which are longer and thinner with suckers only at their club-like ends.[111][112] The vampire squid (Vampyroteuthis) also lacks tentacles but has sensory filaments.[113]
Thecladograms are based on Sanchez et al., 2018, who created amolecular phylogeny based onmitochondrial andnuclear DNA marker sequences.[105] The position of the Eledonidae is from Ibáñez et al., 2020, with a similar methodology.[114] Divergence dates are from Kröger et al., 2011 and Fuchs et al., 2019.[108][107]
The molecular analysis of the octopods shows that the suborder Cirrina (Cirromorphida) and the superfamily Argonautoidea areparaphyletic and are broken up; these names are shown in quotation marks and italics on the cladogram.
Octopuses, like other coleoid cephalopods but unlike morebasal cephalopods or other molluscs, are capable of greaterRNA editing, changing thenucleic acid sequence of theprimary transcript of RNA molecules, than any other organisms. Much editing is done in the nervous system, particularly forexcitability and neuronal morphology. Coleoids rely mostly onADAR enzymes for RNA editing, which requires large,double-stranded RNA structures. The many editing sites areconserved in the coleoid genome and the mutation rates for the sites are hampered. Hence, greater transcriptome plasticity has come at the cost of slower genome evolution.[115]
The octopus genome is unremarkablybilaterian except for large developments of two gene families:protocadherins, which regulate the development of neurons; and theC2H2 zinc-finger transcription factors. Many novel genes in both cephalopods generally and octopus specifically manifest in the animals' skin, suckers, and nervous system.[44]
Relationship to humans
Cultural significance
Minoan clay vase with octopus decoration, c. 1500 BC
Ancient seafaring people were aware of the octopus, as evidenced by artworks and designs. It was depicted on coins during theMinoan civilization possibly as early as 1650 BCE and on pottery inMycenaean Greece around between 1200 and 1100 BCE. A Hawaiiancreation myth suggests that the octopus is the lone survivor of a previous age. The legendary sea monster, thekraken is conceived as octopus-like.[27]: 1, 4–5 Similarly,Medusa was compared to an octopus, with her snake-hair resembling the creature's arms.[116]: 133 TheAkkorokamui is a gigantic octopus-likemonster fromAinu folklore, worshipped inShinto.[117]
In theAsuka-era Japanese legendTaishokan, a female diver battles an octopus to recover a stolen jewel, which became the inspiration forwoodblock printings. Similarly, in the 1973 novelGravity's Rainbow an octopus named Grigori attacks a woman on the beach. A battle with an octopus plays a significant role inVictor Hugo's 1866 bookTravailleurs de la mer (Toilers of the Sea). The octopus continues to be depicted as antagonistic in films such asWake of the Red Witch (1948).[116]: 129–131, 138–139, 145–147
Inpolitical cartoons, octopuses have been used to symbolise empires and large organizations, the arms representing long reach. Octopus also have an erotic appeal. Japanese erotic art,shunga, includesukiyo-e woodblock prints such asKatsushika Hokusai's 1814 printTako to ama (The Dream of the Fisherman's Wife), in which a woman is sexually intertwined with a large and a small octopus. This art style would inspirePablo Picasso's 1903 drawingAn Erotic Drawing: Woman and Octopus.[116]: 126–128 Some individual octopuses gained celebrity status, notablyPaul the Octopus who predicted the winners of the2010 FIFA World Cup.[27]: 3–4
Octopuses generally avoid humans, but some conflictual incidents have been verified. For example, a 2.4-metre (8 ft) Pacific octopus, said to be nearly perfectly camouflaged, "lunged" at a diver and "wrangled" over his camera before it let go. Another diver recorded the encounter on video.[118] All species are venomous, but only blue-ringed octopuses have venom that is lethal to humans.[119] Blue-ringed octopuses rank amongst the most dangerous marine animals; their bites are reported each year across the animals' range from Australia to the eastern Indo-Pacific Ocean. They bite only when provoked or accidentally touched; bites are small and usually painless. The venom appears to be able to penetrate the skin without a puncture, given prolonged contact. It containstetrodotoxin, which causes paralysis by blocking the transmission ofnerve impulses to the muscles. This causes death by respiratory failure leading tocerebral anoxia. No antidote is known, but if breathing can be kept going artificially, patients recover within 24 hours.[120][121] Bites have been recorded from captive octopuses of other species; they leave temporary swellings.[29]: 68
Octopusesare fished around the world and between 1988 and 1995, catches varied between 245,320 and 322,999 metric tons.[122] The world catch peaked in 2007 at 380,000 tons, and had fallen by a tenth by 2012.[123] Methods to capture octopuses include pots,trapping,trawling, snaring, drift fishing, spearing, hooking and catching by hands.[122] Octopuses are alsobycatch.[124] Attempts to farm octopuses commercially are controversial.[125][126]
Octopus is eaten in many cultures, such as those on the Mediterranean and Asian coasts.[127] The arms and other body parts are prepared in ways that vary by species and geography. Live octopuses or their wriggling pieces are consumed assan-nakji in Korean cuisine.[128][129] If not prepared properly, however, the severed arms can choke the diner with their suction cups, causing at least one death in 2010.[130] Animal welfare groups have objected to the live consumption of octopuses on the basis that they can experience pain.[131]
Science and technology
In classical Greece,Aristotle (384–322 BC)commented on their colour-changing abilities, both for camouflage and forsignalling, in hisHistoria animalium: "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 alsowhen alarmed."[132] Aristotle noted that the octopus had a hectocotyl arm and suggested it might be used in reproduction. This claim was widely ignored until the 19th century. It was described in 1829 by the French zoologistGeorges Cuvier, who supposed it to be a parasitic worm, naming it as a new species,Hectocotylus octopodis.[133][134][135] Other zoologists thought it a spermatophore; the German zoologistHeinrich Müller believed it was "designed" to detach during copulation. In 1856, the Danish zoologistJapetus Steenstrup demonstrated that it is used to transfer sperm, and only rarely detaches.[136]
Due to their intelligence, many argue that octopuses should be given protections when used for experiments.[141] In the UK from 1993 to 2012, the common octopus (Octopus vulgaris) was the only invertebrate protected under theAnimals (Scientific Procedures) Act 1986.[142] In 2012, this legislation was extended to include all cephalopods[143] in accordance with a generalEU directive.[144]
Somerobotics research is exploringbiomimicry of octopus features. Octopus arms can move and sense largely autonomously without intervention from the animal's central nervous system. In 2015 a team in Italy built soft-bodied robots able to crawl and swim, requiring only minimal computation.[145][146] In 2017, a German company made an arm with a softpneumatically controlledsilicone gripper fitted with two rows of suckers. It was able to grasp objects such as a metal tube, a magazine, or a ball, and to fill a glass by pouring water from a bottle.[147]
See also
My Octopus Teacher – 2020 documentary film by Pippa Ehrlich and James Reed
^"Tentacle" is a commonumbrella term for cephalopod limbs. Inteuthological context, octopuses have "arms" with suckers along their entire length while "tentacle" is reserved for appendages with suckers only near the end of the limb, which octopuses lack.[4]
^"Octopus". Oxforddictionaries.com. 2014. Archived fromthe original on 30 October 2012. Retrieved4 February 2014.
^Peters, Pam (2004).The Cambridge Guide to English Usage. Cambridge: Cambridge University Press.ISBN0-521-62181-X, p. 388.
^Fowler, Henry Watson (1994).A Dictionary of Modern English Usage. Wordsworth Editions. p. 316.ISBN978-1-85326-318-7.In Latin plurals there are some traps for non-Latinists; the termination of the singular is no sure guide to that of the plural. Most Latin words in-us have plural in-i, but not all, & so zeal not according to knowledge issues in such oddities as...octopi...; as caution the following list may be useful:...octopus,-podes
^Butterfield, Jeremy (2015).Fowler's Dictionary of Modern English Usage. Oxford University Press.ISBN978-0-19-174453-2.The only correct plural in English is octopuses. The Greek original isὀκτώπους,-ποδ- (which would lead to a pedantic English pl. formoctopodes). The pl. formoctopi, which is occasionally heard (mostly in jocular use), though based on modLoctopus, is misconceived
^Cosgrove, J.A. 1987. Aspects of the Natural History ofOctopus dofleini, the Giant Pacific Octopus. MSc Thesis. Department of Biology, University of Victoria (Canada), 101 pp.
^Norman, M. 2000.Cephalopods: A World Guide. ConchBooks, Hackenheim. p. 214.
^High, William L. (1976)."The giant Pacific octopus"(PDF).Marine Fisheries Review.38 (9):17–22. Archived fromthe original(PDF) on 23 January 2017. Retrieved4 November 2016.
^Hague, T; Florini, M; Andrews, P. L. R. (2013). "Preliminary in vitro functional evidence for reflex responses to noxious stimuli in the arms ofOctopus vulgaris".Journal of Experimental Marine Biology and Ecology.447:100–105.Bibcode:2013JEMBE.447..100H.doi:10.1016/j.jembe.2013.02.016.
^Wells, Martin J.; Wells, J. (1972). "Optic glands and the state of the testis inOctopus".Marine Behaviour and Physiology.1 (1–4):71–83.doi:10.1080/10236247209386890.
^Rodaniche, Arcadio F. (1991). "Notes on the behavior of the Larger Pacific Striped Octopus, an undescribed species of the genus Octopus".Bulletin of Marine Science.49: 667.
^Lee, Henry (1875)."V: The octopus out of water".Aquarium Notes – The Octopus; or, the "devil-fish" of fiction and of fact. London: Chapman and Hall. pp. 38–39.OCLC1544491. Retrieved11 September 2015.The marauding rascal had occasionally issued from the water in his tank, and clambered up the rocks, and over the wall into the next one; there he had helped himself to a young lump-fish, and, having devoured it, returned demurely to his own quarters by the same route, with well-filled stomach and contented mind.
^Farto, R.; Armada, S. P.; Montes, M.; Guisande, J. A.; Pérez, M. J.; Nieto, T. P. (2003). "Vibrio lentus associated with diseased wild octopus (Octopus vulgaris)".Journal of Invertebrate Pathology.83 (2):149–156.Bibcode:2003JInvP..83..149F.doi:10.1016/S0022-2011(03)00067-3.PMID12788284.
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