Temporal range: Early Pennsylvanian – Recent
|The common octopus, Octopus vulgaris.|
An octopus (// or //; plural: octopuses, octopi, or octopodes; see below) 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. An octopus has a hard beak, with its mouth at the center point of the arms. An octopus 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 flexible of all invertebrates.
Octopuses inhabit 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.
- 1 Biology
- 2 Etymology and pluralization
- 3 Relationship to humans
- 4 Classification
- 5 See also
- 6 References
- 7 External links
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. 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, 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, 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 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.
An octopus's primary defense is to hide or to disguise itself through camouflage and mimicry. 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 employ smell 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, 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).
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. An 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 an 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 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).
Etymology and pluralization
The term "octopus" is derived, through scientific Latin, from ancient Greek ὀκτώπους ("eight-footed") < ὀκτώ ("eight") and πούς ("foot"). (Ancient Greek also had the form ὀκτάπους, which would give "octapus" in English; cf. Modern Greek χταπόδι < οκταπόδι < οκταπόδιον < ὀκτάπους.)
The usual plural in English is "octopuses" (pronounced /ˈɒktəpʊsɪz/), but the Greek plural form "octopodes" (pronounced /ɒkˈtɒpədiːz/) is sometimes used, though less frequently than in the past. The form "octopi", as if the word were a Latin second-declension noun, is generally considered incorrect, but is in fact used, so that it is registered by the descriptivist Merriam-Webster 11th Collegiate Dictionary, which lists "octopuses" and "octopi", in that order, and Webster's New World College Dictionary, which lists plurals in the order: "octopuses", "octopi", and "octopodes". The Oxford English Dictionary (2008 Draft Revision) also lists "octopuses", "octopi", and "octopodes", in that order, labelling "octopodes" as rare and noting that "octopi" derives from the misapprehension that octōpus is a second-declension Latin noun and stating that, if the word were native to Latin, it would be third declension octōpēs (plural: octōpedes) after the pattern of pēs ("foot", plural pedēs). The New Oxford American Dictionary (3rd Edition 2010) lists only "octopuses" as being the acceptable pluralization, with a usage note indicating "octopodes" as being "still occasionally used", and "octopi" as being "incorrect".
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
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 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.
Akkorokamui is a gigantic octopus-like monster from Ainu folklore, which supposedly lurks in Funka Bay in Hokkaidō and has been sighted in several locations including Taiwan and Korea since the 19th century.
The octopus has a significant role in Victor Hugo's book Travailleurs de la mer (Toilers of the Sea). Ian Fleming's 1966 short story collection Octopussy and The Living Daylights, and the 1983 James Bond film 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.
As a metaphor
Due to having numerous arms that emanate from a common center, the octopus is often used as a metaphor for a group or organization that is perceived as being powerful, manipulative or bent on domination. Use of this terminology is invariably negative and employed by the opponents of the groups or institutions so described.
Octopus is eaten in many cultures. The arms and sometimes other body parts are prepared in various ways, often varying by species or geography.
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.
The variation in size and lifespan among octopus species makes it difficult to know how long a new specimen can naturally be expected to live. That is, a small octopus may be just born or may be an adult, depending on its species. By selecting a well-known species, such as the California two-spot octopus, one can choose a small octopus (around the size of a tennis ball) and be confident it is young with a full life ahead of it.
|Wikispecies has information related to: Octopoda|
- 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
- Family Amphitretidae: telescope octopus
- Family Bolitaenidae: gelatinous octopus
- Family Octopodidae: benthic octopus
- Genus Enteroctopus: giant octopus
- Family Vitreledonellidae: glass octopus
- Superfamily Argonautoida
- Henry the Hexapus, a six-armed octopus
- Legend of the Octopus
- Octopus wrestling
- Paul the Octopus, famous for predicting football results in the 2010 FIFA World Cup
- Kluessendorf, J.; Doyle, P. (2000). "Pohlsepia Mazonensis, an Early 'Octopus' from the Carboniferous of Illinois, USA". Palaeontology 43 (5): 919. doi:10.1111/1475-4983.00155.
- "ITIS Report: Octopoda Leach, 1818". Itis.gov. 2013-04-10. Retrieved 2014-02-04.
- Helsinki.fi, Mikko's Phylogeny Archive: Coleoidea – Recent cephalopods
- "Facts About Octopuses". Retrieved 22 April 2014.
- Unimelb.edu.au, Tentacles of venom: new study reveals all octopuses are venomous, University of Melbourne, Media Release, Wednesday 15 April 2009
- Norman, M. 2000. Cephalopods: A World Guide. ConchBooks, Hackenheim. p. 15. ISBN 978-3-925919-32-9 "There is some confusion around the terms arms versus tentacles. The numerous limbs of nautiluses are called tentacles. The ring of eight limbs around the mouth in cuttlefish, squids and octopuses are called arms. Cuttlefish and squid also have a pair of specialized limbs attached between the bases of the third and fourth arm pairs [...]. These are known as feeding tentacles and are used to shoot out and grab prey."
- Wodinsky, Jerome (2 December 1977). "Hormonal Inhibition of Feeding and Death in Octopus: Control by Optic Gland Secretion". Science 198 (4320): 948–951. doi:10.1126/science.198.4320.948. PMID 17787564. Retrieved 27 November 2011.
- Hamilton, Garry. "What is this octopus thinking?". Archived from the original on 7 April 2012.
- NFW.org?, Is the octopus really the invertebrate intellect of the sea, by Doug Stewart. In: National Wildlife. Feb/Mar 1997, vol.35 no.2. URL is not the source
- "Giant Octopus—Mighty but Secretive Denizen of the Deep". Web.archive.org. 2008-01-02. Retrieved 2014-02-04.
- Slate.com, How Smart is the Octopus?
- "Dynamic model of the octopus arm. I. Biomechanics of the octopus reaching movement". J. Neurophysiol. 94 (2): 1443–58. August 2005. doi:10.1152/jn.00684.2004. PMID 15829594.
- "Nonsomatotopic organization of the higher motor centers in octopus" 19 (19). October 2009. pp. 1632–6. doi:10.1016/j.cub.2009.07.067. PMID 19765993.
- "Octopus intelligence: jar opening". BBC News. 2003-02-25. Retrieved 2014-02-04.
- What behavior can we expect of octopuses?. By Dr. Jennifer Mather, Department of Psychology and Neuroscience, University of Lethbridge and Roland C. Anderson, The Seattle Aquarium.
- "Octopus snatches coconut and runs". BBC News. 2009-12-14. Retrieved 2010-05-20.
- "Coconut shelter: evidence of tool use by octopuses | EduTube Educational Videos". Edutube.org. Retrieved 2014-02-04.
- Finn, J. K.; Tregenza, T; Norman, M. D. (2009). "Defensive tool use in a coconut-carrying octopus". Current Biology 19 (23): R1069–70. doi:10.1016/j.cub.2009.10.052. PMID 20064403.
- "The Animals (Scientific Procedures) Act (Amendment) Order 1993". The National Archives. Retrieved 18 February 2015.
- "The Animals (Scientific Procedures) Act 1986 Amendment Regulations 2012". The National Archives. Retrieved 18 February 2015.
- "DIRECTIVE 2010/63/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL". Article 1, 3(b): Official Journal of the European Union. Retrieved 18 February 2015.
- Hanlon, R.T. & J.B. Messenger 1996. Cephalopod Behaviour. Cambridge University Press, Cambridge.
- Caldwell, R. L. (2005). "An Observation of Inking Behavior Protecting Adult Octopus bocki from Predation by Green Turtle (Chelonia mydas) Hatchlings". Pacific Science 59 (1): 69–72. doi:10.1353/psc.2005.0004.
- Meyers, Nadia. "Tales from the Cryptic: The Common Atlantic Octopus". Southeastern Regional Taxonomic Center. Retrieved 2006-07-27.
- Even Severed Octopus Arms Have Smart Moves. Octopus Chronicles, Scientific American Blog Network.
- Norman, MD; Finn, J; Tregenza, T (September 2001). "Dynamic mimicry in an Indo-Malayan octopus". Proceedings of the Royal Society 268 (1478): 1755–8. doi:10.1098/rspb.2001.1708. PMC 1088805. PMID 11522192.
- Norman, M.D. (2005). "The "Mimic Octopus" (Thaumoctopus mimicus n. gen. et sp.), a new octopus from the tropical Indo-West Pacific (Cephalopoda: Octopodidae)". Molluscan Research 25: 57–70.
- Young, R.E., M. Vecchione & K.M. Mangold 1999. Cephalopoda Glossary. Tree of Life web project.
- Kawamura, G. et al. (2001). "Color Discrimination Conditioning in Two Octopus Octopus aegina and O. vulgaris". Nippon Suisan Gakkashi 67 (1): 35–39. doi:10.2331/suisan.67.35.
- Wells. Martin John. Octopus: physiology and behaviour of an advanced invertebrate. London : Chapman and Hall; New York : distributed in the U.S.A. by Halsted Press, 1978.
- Matt Walker (15 June 2009). "The cephalopods can hear you". BBC. Retrieved 2013-07-19.
- Christine L. Huffard (2006-10-01). "Locomotion by ''Abdopus aculeatus''". Jeb.biologists.org. Retrieved 2014-02-04.
- Huffard, C. L.; Boneka, F; Full, RJ (2005). "Underwater Bipedal Locomotion by Octopuses in Disguise". Science 307 (5717): 1927. doi:10.1126/science.1109616. PMID 15790846.
- Octopuses have only six arms, the other two are actually legs! Hindustan Times, 8/3/2008
- Harmon, Katherine (24 November 2011). "Land-Walking Octopus Explained". Octopus Chronicles. Scientic American blogs. Retrieved 24 November 2011.
- Wood, James B.; Roland C. Anderson (2004). "Interspecific Evaluation of Octopus Escape Behavior". Journal of Applied Animal Welfare Science (Lawrence Erlbaum Associates, Inc.) 7 (2): 95–106. doi:10.1207/s15327604jaws0702_2. PMID 15234886.
- Wassilieff, Maggy; and O’Shea, Steve (2009) "Octopus and squid - Feeding and predation" Te Ara – the Encyclopedia of New Zealand. Updated 2 March 2009.
- Wodinsky, Jerome (1969). "Penetration of the Shell and Feeding on Gastropods by Octopus". Amer. Zool. 9 (3): 997–1010. doi:10.1093/icb/9.3.997.
- Archived Google video of an octopus catching a shark, from The Octopus Show by Mike deGruy
- "Smithsonian National Zoological Park: Giant Pacific Octopus". Nationalzoo.si.edu. Retrieved 2014-02-04.
- Cosgrove, J.A. 1987. Aspects of the Natural History of Octopus dofleini, the Giant Pacific Octopus. M.Sc. Thesis. Department of Biology, University of Victoria (Canada), 101 pp.
- O'Shea, S. (2004). "The giant octopus Haliphron atlanticus (Mollusca : Octopoda) in New Zealand waters". New Zealand Journal of Zoology 31 (1): 7–13. doi:10.1080/03014223.2004.9518353.
- O'Shea, S. (2002). "Haliphron atlanticus — a giant gelatinous octopus". Biodiversity Update 5: 1.
- Norman, M. 2000. Cephalopods: A World Guide. ConchBooks, Hackenheim. p. 214.
- High, W.L. (1976). "The giant Pacific octopus". U.S. National Marine Fisheries Service, Marine Fisheries Review 38 (9): 17–22.
- "Online Etymology Dictionary". Etymonline.com. Retrieved 2014-02-04.
- "Octopus | Define Octopus at Dictionary.com". Dictionary.reference.com. Retrieved 2014-02-04.
- "Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'': ὀκτώπους". Perseus.tufts.edu. Retrieved 2014-02-04.
- Oktapous, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
- Michel, Jean-Baptiste; Shen, Yuan; Aiden, Aviva; Veres, Adrian; Gray, Matthew; Pickett, Joseph; Hoiberg, Dale; Clancy, Dan; Norvig, Peter; Orwant, Jon; Pinker, Steven; Nowak, Martin; The Google Books Team (14 January 2011). "Quantitative Analysis of Culture Using Millions of Digitized Books". Science 331 (6014): 176–182. Relevant data at Google Ngram Viewer.
- "Octopus". Oxforddictionaries.com. 2014-01-30. Retrieved 2014-02-04.
- Peters, Pam (2004). The Cambridge Guide to English Usage. Cambridge: Cambridge University Press. ISBN 0-521-62181-X, p. 388.
- Fowler's Modern English Usage states that the only acceptable plural in English is "octopuses", that "octopi" is misconceived, and "octopodes" pedantic.
- Chambers 21st Century Dictionary (retrieved 19 October 2007)
- Kory Stamper. Ask the editor: octopus. Merriam-Webster. Retrieved 26 June 2013.
- OED.com (subscription required). Retrieved 1 February 2010.
- "centipede". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.
- Angus Stevenson & Christine A. Lindberg, ed. (2010). New Oxford American Dictionary (3rd ed.). Oxford University Press. ISBN 9780195392883.
- C. Michael Hogan. 2007 Knossos fieldnotes, The Modern Antiquarian
- Aristotle (c. 350 BC). Historia Animalium. IX, 622a: 2–10. Cited in Borrelli, Luciana; Gherardi, Francesca; Fiorito, Graziano (2006). A catalogue of body patterning in Cephalopoda. Firenze University Press. ISBN 978-88-8453-377-7. Abstract
- Berrin, Katherine & Larco Museum. The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames and Hudson, 199 7.
- Wilk, Stephen R. (2000). Medusa:Solving the Mystery of the Gorgon. Oxford University Press. ISBN 019988773X.
- Dixon, Roland Burrage (1916). The Mythology of All Races: Oceanic 9. Marshall Jones. p. 15.
- Swancer, Brent via Coleman, Loren. Akkorokamui. Cryptomundo. http://www.cryptomundo.com/cryptozoo-news/akkorokamui
- Chisholm, Hugh, ed. (1911). "Octopus". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- "Sweet Thursday - Plot Synopsis". STEINBECK IN THE SCHOOLS. SAN JOSÉ STATE UNIVERSITY. Retrieved 5 January 2015.
- Starr, Ringo & Bud Cort. "Octopus's Garden". Simon & Shuster. Retrieved 5 January 2015.
- Palmer, Jessica (2010-05-30). "Nazi Tentacles: The octopus as visual metaphor". Scienceblogs.com. Retrieved 2014-02-04.
|The Wikibook Dichotomous Key has a page on the topic of: Octopoda|
Find more about
at Wikipedia's sister projects
|Definitions from Wiktionary|
|Media from Commons|
|News stories from Wikinews|
|Quotations from Wikiquote|
|Source texts from Wikisource|
|Textbooks from Wikibooks|
|Learning resources from Wikiversity|
- 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
- PDF (359 KB)
- Video of walking octopuses