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140-400: (traditional) See § Evolution for families An octopus ( pl. : octopuses or octopodes ) is a soft-bodied, eight-limbed mollusc of the order Octopoda ( / ɒ k ˈ t ɒ p ə d ə / , ok- TOP -ə-də ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids , cuttlefish , and nautiloids . Like other cephalopods, an octopus

280-474: A German pronunciation: [ç] both for the <sch> (standard German [ʃ] ) and the ⟨ch⟩ . Proper names and German loanwords into other languages that have been reborrowed , particularly when they have gone through or are perceived to have gone through the English language are often pronounced " hyperforeign ". Examples include "Hamburger" or the names of German-Americans and

420-405: A mantle with a significant cavity used for breathing and excretion , the presence of a radula (except for bivalves ), and the structure of the nervous system . Other than these common elements, molluscs express great morphological diversity, so many textbooks base their descriptions on a "hypothetical ancestral mollusc" (see image below). This has a single, " limpet -like" shell on top, which

560-435: A 'rake' to comb up filaments from the sea floor. Others feed on macroscopic 'plants' such as kelp, rasping the plant surface with its radula. To employ this strategy, the plant has to be large enough for the mollusc to 'sit' on, so smaller macroscopic plants are not as often eaten as their larger counterparts. Filter feeders are molluscs that feed by straining suspended matter and food particles from water, typically by passing

700-409: A clutch of eggs. Females will spend all their time aerating and protecting their eggs until they are ready to hatch. During senescence, an octopus does not feed and quickly weakens. Lesions begin to form and the octopus literally degenerates. Unable to defend themselves, octopuses often fall prey to predators. This makes most octopuses effectively semelparous . The larger Pacific striped octopus (LPSO)

840-525: A common hypercorrection is the fortition of properly lenis stops, sometimes including aspiration as evidenced by the speech of Günther Beckstein . The digraph <ig> in word-final position is pronounced [ɪç] per the Bühnendeutsch standard, but this pronunciation is frequently perceived as nonstandard and instead realized as [ɪɡ̊] or [ɪk] ( final obstruent devoicing ) even by speakers from dialect areas that pronounce

980-826: A confusion related to the Qamatz Gadol Hebrew vowel, which in the accepted Sephardi Hebrew pronunciation is rendered as /aː/ but which is pronounced /ɔ/ in Ashkenazi Hebrew , and in Hebrew words that also occur in Yiddish . However, the Qamatz Qaṭan vowel, which is visually indistinguishable from the Qamatz Gadol vowel, is rendered as /o/ in both pronunciations. This leads to hypercorrections in both directions. Other hypercorrections occur when speakers of Israeli Hebrew (which

1120-529: A delicacy by humans in many parts of the world, especially the Mediterranean and the Asian seas. The scientific Latin term octopus was derived from Ancient Greek ὀκτώπους ( oktōpous ), a compound form of ὀκτώ ( oktō , 'eight') and πούς ( pous , 'foot'), itself a variant form of ὀκτάπους , a word used for example by Alexander of Tralles ( c.  525 – c.  605 ) for

1260-593: A den without having to retrace their outward route. They are not migratory. Octopuses bring captured prey to the den, where they can eat it safely. Sometimes the octopus catches more prey than it can eat, and the den is often surrounded by a midden of dead and uneaten food items. Other creatures, such as fish, crabs , molluscs and echinoderms , often share the den with the octopus, either because they have arrived as scavengers , or because they have survived capture. On rare occasions, octopuses hunt cooperatively with other species , with fish as their partners. They regulate

1400-442: A fish, and are enclosed in a cartilaginous capsule fused to the cranium. The cornea is formed from a translucent epidermal layer; the slit-shaped pupil forms a hole in the iris just behind the cornea. The lens is suspended behind the pupil; photoreceptive retinal cells cover the back of the eye. The pupil can be adjusted in size; a retinal pigment screens incident light in bright conditions. Some species differ in form from

1540-435: A group comprising cephalopods. Molluscus is used in classical Latin as an adjective only with nux ( nut ) to describe a particular type of soft nut. The use of mollusca in biological taxonomy by Jonston and later Linnaeus may have been influenced by Aristotle 's τὰ μαλάκια ta malákia (the soft ones; < μαλακός malakós "soft"), which he applied inter alia to cuttlefish . The scientific study of molluscs

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1680-418: A hard shell use calcite (sometimes with traces of aragonite) to construct the eggshells. The shell consists of three layers: the outer layer (the periostracum ) made of organic matter, a middle layer made of columnar calcite , and an inner layer consisting of laminated calcite, often nacreous . In some forms the shell contains openings. In abalones there are holes in the shell used for respiration and

1820-413: A hole in the shell to inject a nerve toxin . It used to be thought that the hole was drilled 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. It takes about three hours for O. vulgaris to create a 0.6 mm (0.024 in) hole. Once the shell is penetrated,

1960-401: A jet of water from the mantle through the siphon into the sea. The physical principle behind this is that the force required to accelerate the water through the orifice produces a reaction that propels the octopus in the opposite direction. 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,

2100-514: A mantle pressure so high as to stop the heart from beating, resulting in a progressive oxygen deficit. Cirrate octopuses cannot produce jet propulsion and rely on their fins for swimming. They have neutral buoyancy and drift through the water with the fins extended. 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 producing peristaltic waves . This moves

2240-403: A maximum of 120,000 species. The total number of described species is difficult to estimate because of unresolved synonymy . In 1969, David Nicol estimated the probable total number of living mollusc species at 107,000 of which were about 12,000  fresh-water gastropods and 35,000  terrestrial . The Bivalvia would comprise about 14% of the total and the other five classes less than 2% of

2380-399: A number of paired ganglia, the visceral cords serving the internal organs and the pedal ones serving the foot. Most pairs of corresponding ganglia on both sides of the body are linked by commissures (relatively large bundles of nerves). The ganglia above the gut are the cerebral, the pleural, and the visceral, which are located above the esophagus (gullet). The pedal ganglia, which control

2520-407: A pair of statocysts , which act as balance sensors. In gastropods, it secretes mucus as a lubricant to aid movement. In forms having only a top shell, such as limpets , the foot acts as a sucker attaching the animal to a hard surface, and the vertical muscles clamp the shell down over it; in other molluscs, the vertical muscles pull the foot and other exposed soft parts into the shell. In bivalves,

2660-678: A rasping "tongue", the radula, and a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles. The generalized mollusc has two paired nerve cords , or three in bivalves . The brain , in species that have one, encircles the esophagus . Most molluscs have eyes , and all have sensors to detect chemicals, vibrations, and touch . The simplest type of molluscan reproductive system relies on external fertilization , but more complex variations occur. Nearly all produce eggs , from which may emerge trochophore larvae , more complex veliger larvae, or miniature adults. The coelomic cavity

2800-728: A real or imagined grammatical rule is applied in an inappropriate context, so that an attempt to be "correct" leads to an incorrect result. It does not occur when a speaker follows "a natural speech instinct", according to Otto Jespersen and Robert J. Menner. Hypercorrection can be found among speakers of less prestigious language varieties who attempt to produce forms associated with high-prestige varieties, even in situations where speakers of those varieties would not. Some commentators call such production hyperurbanism . Hypercorrection can occur in many languages and wherever multiple languages or language varieties are in contact. Studies in sociolinguistics and applied linguistics have noted

2940-424: A risk of food poisoning, and many jurisdictions have regulations to reduce this risk. Molluscs have, for centuries, also been the source of important luxury goods, notably pearls , mother of pearl , Tyrian purple dye, and sea silk . Their shells have also been used as money in some preindustrial societies. A handful of mollusc species are sometimes considered hazards or pests for human activities. The bite of

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3080-496: A shell (secondarily absent in a number of taxonomic groups, such as the nudibranchs ) that consists of mainly chitin and conchiolin (a protein hardened with calcium carbonate ), except the outermost layer, which in almost all cases is all conchiolin (see periostracum ). Molluscs never use phosphate to construct their hard parts, with the questionable exception of Cobcrephora . While most mollusc shells are composed mainly of aragonite , those gastropods that lay eggs with

3220-486: A shelter, an example of tool use . Octopuses use camouflage when hunting and to avoid predators. To do this, they use specialised skin cells that change the appearance of the skin by adjusting its colour, opacity, or reflectivity. 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. This colour-changing ability

3360-404: A single indisputable record of an octopus in the hadal zone ; a species of Grimpoteuthis (dumbo octopus) photographed at 6,957 m (22,825 ft). No species are known to live in fresh water. Most species are solitary when not mating, though a few are known to occur in high densities and with frequent interactions, such as signaling, mate defending and evicting individuals from dens. This

3500-456: A singular gill. Generally, the gills are rather like feathers in shape, although some species have gills with filaments on only one side. They divide the mantle cavity so water enters near the bottom and exits near the top. Their filaments have three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clean. If the osphradia detect noxious chemicals or possibly sediment entering

3640-422: A surface, the orifice between the two structures is sealed. The infundibulum provides adhesion while the acetabulum remains free, and muscle contractions allow for attachment and detachment. Each of the eight arms senses and responds to light, allowing the octopus to control the limbs even if its head is obscured. The eyes of the octopus are large and at the top of the head. They are similar in structure to those of

3780-433: A systemic or main heart that circulates blood around the body and two branchial or gill hearts that pump it through each of the two gills. The systemic heart becomes inactive when the animal is swimming. Thus the octopus tires quickly and prefers to crawl. Octopus blood contains the copper -rich protein haemocyanin to transport oxygen. This makes the blood very viscous and it requires considerable pressure to pump it around

3920-433: A water jet. Before it leaves the funnel, the ink passes through glands which mix it with mucus, creating a thick, dark blob which allows the animal to escape from a predator. The main pigment in the ink is melanin , which gives it its black colour. Cirrate octopuses usually lack the ink sac. Octopuses are gonochoric and have a single, posteriorly-located gonad which is associated with the coelom . The testis in males and

4060-445: Is Octopus wolfi , which is around 2.5 cm (1 in) and weighs less than 1 g (0.035 oz). The octopus is bilaterally symmetrical along its dorso-ventral (back to belly) axis; the head and foot are at one end of an elongated body and function as the anterior (front) of the animal. The head includes the mouth and brain. The foot has evolved into a set of flexible, prehensile appendages , known as "arms", that surround

4200-426: Is bilaterally symmetric with two eyes and a beaked mouth at the centre point of the eight limbs. The soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion , by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among

4340-427: Is octopuses , that octopi is misconceived, and octopodes pedantic ; the last is nonetheless used frequently enough to be acknowledged by the descriptivist Merriam-Webster 11th Collegiate Dictionary and Webster's New World College Dictionary . The Oxford English Dictionary lists octopuses , octopi , and octopodes , in that order, reflecting frequency of use, calling octopodes rare and noting that octopi

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4480-415: Is a hemocoel through which blood and coelomic fluid circulate and which encloses most of the other internal organs. These hemocoelic spaces act as an efficient hydrostatic skeleton . The blood of these molluscs contains the respiratory pigment hemocyanin as an oxygen -carrier. The heart consists of one or more pairs of atria ( auricles ), which receive oxygenated blood from the gills and pump it to

4620-812: Is a second declension word of Latin origin when in fact it is third declension and comes from Greek . Sociolinguists often note hypercorrection in terms of pronunciation (phonology). For example, William Labov noted that all of the English speakers he studied in New York City in the 1960s tended to pronounce words such as hard as rhotic (pronouncing the "R" as / h ɑːr d / rather than / h ɑː d / ) more often when speaking carefully. Furthermore, middle class speakers had more rhotic pronunciation than working class speakers did. However, lower-middle class speakers had more rhotic pronunciation than upper-middle class speakers. Labov suggested that these lower-middle class speakers were attempting to emulate

4760-421: Is a third-declension noun. Historically, the first plural to commonly appear in English language sources, in the early 19th century, is the latinate form octopi , followed by the English form octopuses in the latter half of the same century. The Hellenic plural is roughly contemporary in usage, although it is also the rarest. Fowler's Modern English Usage states that the only acceptable plural in English

4900-437: Is accordingly called malacology . The name Molluscoida was formerly used to denote a division of the animal kingdom containing the brachiopods , bryozoans , and tunicates , the members of the three groups having been supposed to somewhat resemble the molluscs. As now known, these groups have no relation to molluscs, and very little to one another, so the name Molluscoida has been abandoned. The most universal features of

5040-449: Is also used to communicate with or warn other octopuses. The energy cost of the complete activation of the chromatophore system is very high equally being nearly as much as all the energy used by an octopus at rest. 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,

5180-523: Is an endemic snail species of the Eastern Alps . There is strong evidence for self-fertilization in the easternmost snail populations of this species. The most basic molluscan larva is a trochophore , which is planktonic and feeds on floating food particles by using the two bands of cilia around its "equator" to sweep food into the mouth, which uses more cilia to drive them into the stomach, which uses further cilia to expel undigested remains through

5320-498: Is an exception, as it can reproduce repeatedly over a life of around two years. Octopus reproductive organs mature due to the hormonal influence of the optic gland but result in the inactivation of their digestive glands. Unable to feed, the octopus typically dies of starvation. Experimental 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. It has been proposed that

5460-402: Is associated with the odontophore , a cartilaginous supporting organ. The radula is unique to the molluscs and has no equivalent in any other animal. Molluscs' mouths also contain glands that secrete slimy mucus , to which the food sticks. Beating cilia (tiny "hairs") drive the mucus towards the stomach, so the mucus forms a long string called a "food string". At the tapered rear end of

5600-559: Is based on Sephardic) attempt to pronounce Ashkenazi Hebrew, for example for religious purposes. The month of Shevat ( שבט ‎) is mistakenly pronounced Shvas , as if it were spelled * שְׁבַת ‎. In an attempt to imitate Polish and Lithuanian dialects, qamatz (both gadol and qatan ), which would normally be pronounced [ɔ] , is hypercorrected to the pronunciation of holam , [ɔj] , rendering גדול ‎ ('large') as goydl and ברוך ‎ ('blessed') as boyrukh . In some Spanish dialects,

5740-519: Is based on a misunderstanding. The New Oxford American Dictionary (3rd Edition, 2010) lists octopuses as the only acceptable pluralisation, and indicates that octopodes is still occasionally used, but that octopi is incorrect. 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

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5880-409: Is broken down and is forced into the oesophagus by two lateral extensions of the esophageal side walls in addition to the radula. From there it is transferred to the gastrointestinal tract , which is mostly suspended from the roof of the mantle cavity by numerous membranes. The tract consists of a crop , where the food is stored; a stomach, where food is ground down; a caecum where the now sludgy food

6020-441: Is complex, only part of which is localised in its brain, which is contained in a cartilaginous capsule. Two-thirds of an octopus's neurons are in the nerve cords of its arms. This allows their arms to perform complex reflex actions without input from the brain. Unlike vertebrates, the complex motor skills of octopuses are not organised in their brains via internal somatotopic maps of their bodies. The nervous system of cephalopods

6160-427: Is formally spelt de in the subjective case and dem in the objective case. Informally it can be spelled dom (" Dom tycker om mig ."), yet dom is only acceptable in spoken language. When spelt more formally, they are often confused with each other. (" De tycker om mig ." as a correct form, compared to " Dem tycker om mig "* as an incorrect form in this case). As an object form, using dem in

6300-447: Is likely the result of abundant food supplies combined with limited den sites. The LPSO has been described as particularly social, living in groups of up to 40 individuals. Octopuses hide in dens, which are typically crevices in rocky outcrops or other hard structures, though some species burrow into sand or mud. Octopuses are not territorial but generally remain in a home range; they may leave in search of food. They can navigate back to

6440-449: Is made of proteins and chitin reinforced with calcium carbonate , and is secreted by a mantle covering the whole upper surface. The underside of the animal consists of a single muscular "foot". Although molluscs are coelomates , the coelom tends to be small. The main body cavity is a hemocoel through which blood circulates; as such, their circulatory systems are mainly open . The "generalized" mollusc's feeding system consists of

6580-414: Is never pronounced that way, however). The conjunction och is also sometimes pronounced the same way. Both pronunciations can informally be spelt å . (" Jag älskar å fiska å jag tycker också om å baka .") When spelt more formally, the infinitive marker /'ɔ/ is sometimes misspelt och . (" Få mig och hitta tillbaka .*") The third person plural pronoun, pronounced dom in many dialects,

6720-433: Is one of the largest invertebrates , surpassed in weight but not in length by the colossal squid . Freshwater and terrestrial molluscs appear exceptionally vulnerable to extinction. Estimates of the numbers of non-marine molluscs vary widely, partly because many regions have not been thoroughly surveyed. There is also a shortage of specialists who can identify all the animals in any one area to species. However, in 2004

6860-662: Is reduced. They have an open circulatory system and kidney-like organs for excretion. Good evidence exists for the appearance of gastropods, cephalopods , and bivalves in the Cambrian period, 541–485.4 million years ago. However, the evolutionary history both of molluscs' emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still subjects of vigorous debate among scientists. Molluscs have been and still are an important food source for humans. Toxins that can accumulate in certain molluscs under specific conditions create

7000-420: Is secreted by a mantle covering the upper surface. The underside consists of a single muscular "foot". The visceral mass, or visceropallium, is the soft, nonmuscular metabolic region of the mollusc. It contains the body organs. The mantle cavity, a fold in the mantle, encloses a significant amount of space. It is lined with epidermis, and is exposed, according to habitat , to sea, fresh water or air. The cavity

7140-526: Is sometimes called hyperurbanism , defined by Kingsley Amis as an "indulged desire to be posher than posh". In 2004, Jack Lynch, assistant professor of English at Rutgers University , said on Voice of America that the correction of the subject-positioned "you and me" to "you and I" leads people to "internalize the rule that 'you and I' is somehow more proper, and they end up using it in places where they should not – such as 'he gave it to you and I' when it should be 'he gave it to you and me.' However,

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7280-497: Is sorted into fluids and particles and which plays an important role in absorption; the digestive gland , where liver cells break down and absorb the fluid and become "brown bodies"; and the intestine, where the accumulated waste is turned into faecal ropes by secretions and blown out of the funnel via the rectum. During osmoregulation , fluid is added to the pericardia of the branchial hearts. The octopus has two nephridia (equivalent to vertebrate kidneys) which are associated with

7420-543: Is the most complex of all invertebrates. The giant nerve fibers of the cephalopod mantle have been widely used for many years as experimental material in neurophysiology ; their large diameter (due to lack of myelination ) makes them relatively easy to study compared with other animals. Like other cephalopods, octopuses have camera-like eyes, and can distinguish the polarisation of light. Colour vision appears to vary from species to species, for example, being present in O. aegina but absent in O. vulgaris . Opsins in

7560-550: Is transmitted to humans by water snail hosts, and affects about 200 million people. Snails and slugs can also be serious agricultural pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems . The words mollusc and mollusk are both derived from the French mollusque , which originated from the post-classical Latin mollusca , from mollis , soft, first used by J. Jonston (Historiæ Naturalis, 1650) to describe

7700-501: 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 ungainly gait supported by its remaining arms held rigid. Octopuses are highly intelligent . Maze and problem-solving experiments have shown evidence of a memory system that can store both short- and long-term memory . Young octopuses learn nothing from their parents, as adults provide no parental care beyond tending to their eggs until

7840-480: The IUCN Red List of Threatened Species included nearly 2,000 endangered non-marine molluscs. For comparison, the great majority of mollusc species are marine, but only 41 of these appeared on the 2004 Red List. About 42% of recorded extinctions since the year 1500 are of molluscs, consisting almost entirely of non-marine species. Because of the great range of anatomical diversity among molluscs, many textbooks start

7980-405: The blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last over a month. Stings from a few species of large tropical cone shells of the family Conidae can also kill, but their sophisticated, though easily produced, venoms have become important tools in neurological research. Schistosomiasis (also known as bilharzia, bilharziosis, or snail fever)

8120-793: The blue-ringed octopuses are known to be deadly to humans. Octopuses appear in mythology as sea monsters like the Kraken of Norway and the Akkorokamui of the Ainu , and possibly the Gorgon of ancient Greece . 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 and considered

8260-462: The coelom , a small cavity that surrounds the heart, into which they shed ova or sperm . The nephridia extract the gametes from the coelom and emit them into the mantle cavity. Molluscs that use such a system remain of one sex all their lives and rely on external fertilization . Some molluscs use internal fertilization and/or are hermaphrodites , functioning as both sexes; both of these methods require more complex reproductive systems. C. obtusus

8400-413: The ovary in females bulges into the gonocoel and the gametes are released here. The gonocoel is connected by the gonoduct to the mantle cavity , which it enters at the gonopore . An optic gland creates hormones that cause the octopus to mature and age and stimulate gamete production. The gland may be triggered by environmental conditions such as temperature, light and nutrition, which thus control

8540-454: The species composition of the hunting group   —   and the behavior of their partners   —   by punching them. Nearly all octopuses are predatory; bottom-dwelling octopuses eat mainly crustaceans , polychaete worms , and other molluscs such as whelks and clams ; open-ocean octopuses eat mainly prawns, fish and other cephalopods. Major items in the diet of the giant Pacific octopus include bivalve molluscs such as

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8680-400: The ventricle , which pumps it into the aorta (main artery ), which is fairly short and opens into the hemocoel. The atria of the heart also function as part of the excretory system by filtering waste products out of the blood and dumping it into the coelom as urine . A pair of metanephridia ("little kidneys") to the rear of and connected to the coelom extracts any re-usable materials from

8820-483: The adults. In the argonaut (paper nautilus), the female secretes a fine, fluted, papery shell in which the eggs are deposited and in which she also resides while floating in mid-ocean. In this she broods the young, and it also serves as a buoyancy aid allowing her to adjust her depth. The male argonaut is minute by comparison and has no shell. Octopuses have short lifespans, and some species complete their lifecycles in only six months. The Giant Pacific octopus , one of

8960-412: The anus. New tissue grows in the bands of mesoderm in the interior, so the apical tuft and anus are pushed further apart as the animal grows. The trochophore stage is often succeeded by a veliger stage in which the prototroch , the "equatorial" band of cilia nearest the apical tuft, develops into the velum ("veil"), a pair of cilia-bearing lobes with which the larva swims. Eventually, the larva sinks to

9100-402: The arms are covered with circular, adhesive suckers. The suckers allow the octopus to anchor itself or to manipulate objects. Each sucker is usually circular and bowl-like and has two distinct parts: an outer shallow cavity called an infundibulum and a central hollow cavity called an acetabulum , both of which are thick muscles covered in a protective chitinous cuticle. When a sucker attaches to

9240-431: The blood. Respiration involves drawing water into the mantle cavity through an aperture, passing it through the gills, and expelling it through the siphon. The ingress of water is achieved by contraction of radial muscles in the mantle wall, and flapper valves shut when strong circular muscles force the water out through the siphon. Extensive connective tissue lattices support the respiratory muscles and allow them to expand

9380-514: The body is made of soft tissue allowing it to lengthen, contract, and contort itself. The octopus can squeeze through tiny gaps; even the larger species can pass through an opening close to 2.5 cm (1 in) in diameter. Lacking skeletal support, the arms work as muscular hydrostats and contain longitudinal, transverse and circular muscles around a central axial nerve. They can extend and contract, twist to left or right, bend at any place in any direction or be held rigid. The interior surfaces of

9520-410: The body slowly. In 2005, Adopus aculeatus and veined octopus ( Amphioctopus marginatus ) were found to walk on two arms, while at the same time mimicking plant matter. This form of locomotion allows these octopuses to move quickly away from a potential predator without being recognised. Some species of octopus can crawl out of the water briefly, which they may do between tide pools. "Stilt walking"

9660-672: The body structure of molluscs are a mantle with a significant body cavity used for breathing and excretion , and the organization of the nervous system. Many have a calcareous shell. Molluscs have developed such a varied range of body structures, finding synapomorphies (defining characteristics) to apply to all modern groups is difficult. The most general characteristic of molluscs is they are unsegmented and bilaterally symmetrical. The following are present in all modern molluscs: Other characteristics that commonly appear in textbooks have significant exceptions: Estimates of accepted described living species of molluscs vary from 50,000 to

9800-418: The body. The blood vessels consist of arteries, capillaries and veins and are lined with a cellular endothelium which is quite unlike that of most other invertebrates . The blood circulates through the aorta and capillary system, to the vena 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

9940-434: The body; octopuses' blood pressures can exceed 75 mmHg (10 kPa). In cold conditions with low oxygen levels, haemocyanin transports oxygen more efficiently than haemoglobin . The haemocyanin is dissolved in the plasma instead of being carried within blood cells and gives the blood a bluish colour. The systemic heart has muscular contractile walls and consists of a single ventricle and two atria, one for each side of

10080-406: The branchial hearts; these and their associated ducts connect the pericardial cavities with the mantle cavity. Before reaching the branchial heart, each branch of the vena cava expands to form renal appendages which are in direct contact with the thin-walled nephridium. The urine is first formed in the pericardial cavity, and is modified by excretion, chiefly of ammonia, and selective absorption from

10220-518: The cockle Clinocardium nuttallii , clams and scallops and crustaceans such as crabs and spider crabs . Prey that it is likely to reject include moon snails because they are too large and limpets , rock scallops , chitons and abalone , because they are too securely fixed to the rock. Small cirrate octopuses such as those of the genera Grimpoteuthis and Opisthoteuthis typically prey on polychaetes, copepods , amphipods and isopods . A benthic (bottom-dwelling) octopus typically moves among

10360-400: The cold, ocean depths. The spoon-armed octopus ( Bathypolypus arcticus ) is found at depths of 1,000 m (3,300 ft), and Vulcanoctopus hydrothermalis lives near hydrothermal vents at 2,000 m (6,600 ft). The cirrate species are often free-swimming and live in deep-water habitats. Although several species are known to live at bathyal and abyssal depths, there is only

10500-478: The common octopus. The standard pluralised form of octopus in English is octopuses ; the Ancient Greek plural ὀκτώποδες , octopodes ( / ɒ k ˈ t ɒ p ə d iː z / ), has also been used historically. The alternative plural octopi is usually considered incorrect because it wrongly assumes that octopus is a Latin second-declension -us noun or adjective when, in either Greek or Latin, it

10640-467: The companies named after them, even if they were or are first generation immigrants. Some German speakers pronounce the metal umlaut as if it were a "normal" German umlaut. For example, when Mötley Crüe visited Germany, singer Vince Neil said the band could not figure out why "the crowds were chanting, 'Mutley Cruh! Mutley Cruh! ' " In Swedish, the word att is sometimes pronounced / ɔ / when used as an infinitive marker (its conjunction homograph

10780-522: The digraph [ɪç] or [ɪʃ] . Palatinate German language speakers are among those who pronounce both the digraph ⟨ch⟩ and the trigraph ⟨sch⟩ as [ʃ] . A common hypercorrection is to produce [ç] even where standard German has [ʃ] such as in Helmut Kohl 's hypercorrect rendering of "Geschichte", the German word for "history" with

10920-413: The distribution of a pattern found in loanwords and extending it to other environments. The result of this process does not reflect the rules of either language. For example, habanero is sometimes pronounced as though it were spelled "habañero", in imitation of other Spanish words like jalapeño and piñata . Machismo is sometimes pronounced "makizmo", apparently as if it were Italian, rather than

11060-401: The eggs to completely develop. The female aerates them and keeps them clean; if left untended, many will die. She does not feed during this time and dies soon after. Males become senescent and die a few weeks after mating. The eggs have large yolks; cleavage (division) is superficial and a germinal disc develops at the pole. During gastrulation , the margins of this grow down and surround

11200-427: The female's mantle cavity, after which he becomes senescent and dies, while the female deposits fertilised eggs in a den and cares for them until they hatch, after which she also dies. Strategies to defend themselves against predators include the expulsion of ink , the use of camouflage and threat displays , the ability to jet quickly through the water and hide, and even deceit. All octopuses are venomous , but only

11340-441: 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 for the species, which in the giant Pacific octopus is 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. A complex hydraulic mechanism releases

11480-505: The final intervocalic /d/ ( [ð] ) is dropped, such as in pescado (fish), which would typically be pronounced [pesˈkaðo] but can be manifested as [pesˈkao] dialectically. Speakers sensitive to this variation may insert a /d/ intervocalically into a word without such a consonant, such as in the case of bacalao (cod), correctly pronounced [bakaˈlao] but occasionally hypercorrected to [bakaˈlaðo] . Outside Spain and in Andalusia ,

11620-421: The foot is adapted for burrowing into the sediment; in cephalopods it is used for jet propulsion, and the tentacles and arms are derived from the foot. Most molluscs' circulatory systems are mainly open , except for cephalopods , whose circulatory systems are closed . Although molluscs are coelomates , their coeloms are reduced to fairly small spaces enclosing the heart and gonads. The main body cavity

11760-422: The foot, are below the esophagus and their commissure and connectives to the cerebral and pleural ganglia surround the esophagus in a circumesophageal nerve ring or nerve collar . The acephalic molluscs (i.e., bivalves) also have this ring but it is less obvious and less important. The bivalves have only three pairs of ganglia— cerebral, pedal, and visceral— with the visceral as the largest and most important of

11900-405: The gills; skin oxygen uptake also increases. When it is resting after a meal, absorption through the skin can drop to 3% of its total oxygen uptake. The digestive system of the octopus begins with the buccal mass which consists of the mouth with its chitinous beak, the pharynx, radula and salivary glands. The radula is a spiked, muscular tongue-like organ with multiple rows of tiny teeth. Food

12040-404: The initial h from words; e.g., have becomes ' ave . A hypercorrection associated with this is H-adding , adding an initial h to a word which would not normally have one. An example of this can be found in the speech of the character Parker in the marionette TV series Thunderbirds , e.g., "We'll 'ave the haristocrats 'ere soon" (from the episode "Vault of Death"). Parker's speech

12180-528: The language in more formal occasions, thus using the locative even when the accusative should be used (typically, when indicating direction rather than location): " Izlazim na kolovozu " instead of " izlazim na kolovoz ". Ghil'ad Zuckermann argues that the following hypercorrect pronunciations in Israeli Hebrew are "snobbatives" (from snob + -ative , modelled upon comparatives and superlatives ): The last two hypercorrection examples derive from

12320-432: The letter "U", the letter "W", or a dumbbell , as well as the need for colourful mating displays. Attached to the brain are two organs called statocysts (sac-like structures containing a mineralised mass and sensitive hairs), that allow the octopus to sense the orientation of its body. They provide information on the position of the body relative to gravity and can detect angular acceleration. An autonomic response keeps

12460-458: The linguists Rodney Huddleston and Geoffrey K. Pullum write that utterances such as "They invited Sandy and I" are "heard constantly in the conversation of people whose status as speakers of Standard English is clear" and that "[t]hose who condemn it simply assume that the case of a pronoun in a coordination must be the same as when it stands alone. Actual usage is in conflict with this assumption." Some British accents, such as Cockney , drop

12600-475: The living molluscs. In 2009, Chapman estimated the number of described living mollusc species at 85,000. Haszprunar in 2001 estimated about 93,000 named species, which include 23% of all named marine organisms. Molluscs are second only to arthropods in numbers of living animal species — far behind the arthropods' 1,113,000 but well ahead of chordates ' 52,000. About 200,000 living species in total are estimated, and 70,000 fossil species, although

12740-421: The mantle can take on the spiky appearance of algae; in others, skin anatomy is limited to relatively uniform shades of one colour with limited skin texture. Octopuses that are diurnal and live in shallow water have evolved more complex skin than their nocturnal and deep-sea counterparts. A "moving rock" trick involves the octopus mimicking a rock and then inching across the open space with a speed matching that of

12880-468: The mantle cavity, the gills' cilia may stop beating until the unwelcome intrusions have ceased. Each gill has an incoming blood vessel connected to the hemocoel and an outgoing one to the heart. Molluscs use intracellular digestion . Most molluscs have muscular mouths with radulae , "tongues", bearing many rows of chitinous teeth, which are replaced from the rear as they wear out. The radula primarily functions to scrape bacteria and algae off rocks, and

13020-422: The most neurologically advanced of all invertebrates —and either the giant squid or the colossal squid is the largest known extant invertebrate species. The gastropods ( snails , slugs and abalone ) are by far the most diverse class and account for 80% of the total classified molluscan species. The four most universal features defining modern molluscs are a soft body composed almost entirely of muscle ,

13160-410: The most intelligent and behaviourally diverse of all invertebrates . Octopuses inhabit various regions of the ocean , including coral reefs , pelagic waters, and the seabed ; some live in the intertidal zone and others at abyssal depths . Most species grow quickly, mature early, and are short-lived. In most species, the male uses a specially adapted arm to deliver a bundle of sperm directly into

13300-433: The mouth and are attached to each other near their base by a webbed structure. The arms can be described based on side and sequence position (such as L1, R1, L2, R2) and divided into four pairs. The two rear appendages are generally used to walk on the sea floor, while the other six are used to forage for food. The bulbous and hollow mantle is fused to the back of the head and is known as the visceral hump; it contains most of

13440-543: The muscle cells that control the suckers in most species have been replaced with photophores which are believed to fool prey by directing them to the mouth, making them one of the few bioluminescent octopuses. 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, followed by swimming and crawling. When in no hurry, they usually crawl on either solid or soft surfaces. Several arms are extended forward, some of

13580-441: The naturally short lifespan may be functional to prevent rapid overpopulation. Octopuses live in every ocean, and different species have adapted to different marine habitats . As juveniles, common octopuses inhabit shallow tide pools . The Hawaiian day octopus ( Octopus cyanea ) lives on coral reefs; argonauts drift in pelagic waters . Abdopus aculeatus mostly lives in near-shore seagrass beds. Some species are adapted to

13720-572: The new language (a situation known as language transfer ). The effect can occur, for example, when a student of a new language has learned that certain sounds of their original language must usually be replaced by another in the studied language, but has not learned when not to replace them. English has no authoritative body or language academy codifying norms for standard usage , unlike some other languages . Nonetheless, within groups of users of English, certain usages are considered unduly elaborate adherences to formal rules. Such speech or writing

13860-908: The number of classes of molluscs; for example, the table below shows seven living classes, and two extinct ones. Although they are unlikely to form a clade, some older works combine the Caudofoveata and Solenogasters into one class, the Aplacophora . Two of the commonly recognized "classes" are known only from fossils. Brachiopods Bivalves Monoplacophorans ("limpet-like", "living fossils") Scaphopods (tusk shells) Gastropods ( snails , slugs , limpets , sea hares ) Cephalopods ( nautiloids , ammonites , octopus , squid , etc.) Aplacophorans (spicule-covered, worm-like) Polyplacophorans (chitons) Wiwaxia Halkieria † Orthrozanclus † Odontogriphus Hypercorrection Linguistic hypercorrection occurs when

14000-524: The oceans, from the seashores to the abyssal zone , but some form a significant part of the freshwater fauna and the terrestrial ecosystems . Molluscs are extremely diverse in tropical and temperate regions, but can be found at all latitudes . About 80% of all known mollusc species are gastropods. Cephalopoda such as squid , cuttlefish , and octopuses are among the most neurologically advanced of all invertebrates. The giant squid , which until recently had not been observed alive in its adult form,

14140-401: The octopus's eyes oriented so that the pupil is always horizontal. Octopuses may also use the statocyst to hear sound. The common octopus can hear sounds between 400 Hz and 1000 Hz, and hears best at 600 Hz. Octopuses have an excellent somatosensory system . Their suction cups are equipped with chemoreceptors so they can taste what they touch. Octopus arms move easily because

14280-407: The overapplication of rules of phonology , syntax , or morphology , resulting either from different rules in varieties of the same language or second-language learning . An example of a common hypercorrection based on application of the rules of a second (i.e., new, foreign) language is the use of octopi for the plural of octopus in English; this is based on the faulty assumption that octopus

14420-411: The part of the mantle cavity, is swept by the outgoing "lane" of the current created by the gills. Carnivorous molluscs usually have simpler digestive systems. As the head has largely disappeared in bivalves, the mouth has been equipped with labial palps (two on each side of the mouth) to collect the detritus from its mucus. The cephalic molluscs have two pairs of main nerve cords organized around

14560-457: The phonemes /θ/ and /s/ have merged, mostly into the realization [ s ] but ceceo , i.e. the pronunciation of both as [ s̟ ] is found in some areas as well, primarily parts of Andalusia. Speakers of varieties that have [ s ] in all cases will frequently produce [ θ ] even in places where peninsular Spanish has [ s ] when trying to imitate a peninsular accent. As Spanish orthography distinguishes

14700-527: The phonetic English pronunciation which resembles the original Spanish word, /mɑːˈtʃiz.mo/ . Similarly, the z in chorizo is sometimes pronounced as /ts/ (as if it were Italian), whereas the original Spanish pronunciation has /θ/ or /s/ . Some English-Spanish cognates primarily differ by beginning with s instead of es , such as the English word spectacular and the Spanish word espectacular . A native Spanish speaker may conscientiously hypercorrect for

14840-415: The prey dies almost instantaneously, its muscles relax, and the soft tissues are easy for the octopus to remove. Crabs may also be treated in this way; tough-shelled species are more likely to be drilled, and soft-shelled crabs are torn apart. Some species have other modes of feeding. Grimpoteuthis has a reduced or non-existent radula and swallows prey whole. In the deep-sea genus Stauroteuthis , some of

14980-448: The pronunciation of upper-middle class speakers, but were actually over-producing the very noticeable R-sound. A common source of hypercorrection in English speakers' use of the language's morphology and syntax happens in the use of pronouns (see § Personal pronouns ) . Hypercorrection can also occur when learners of a new-to-them (second, foreign) language try to avoid applying grammatical rules from their native language to

15120-548: The proportion of undescribed species is very high. Many taxa remain poorly studied. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms . They are highly diverse, not just in size and anatomical structure, but also in behaviour and habitat , as numerous groups are freshwater and even terrestrial species. The phylum is typically divided into 7 or 8 taxonomic classes , of which two are entirely extinct . Cephalopod molluscs, such as squid , cuttlefish , and octopuses , are among

15260-440: The release of egg and sperm, in the nautilus a string of tissue called the siphuncle goes through all the chambers, and the eight plates that make up the shell of chitons are penetrated with living tissue with nerves and sensory structures. The body of a mollusc has a ventral muscular foot, which is adapted to different purposes (locomotion, grasping the substratum, burrowing or feeding) in different classes. The foot carries

15400-424: The renal appendages, as it is passed along the associated duct and through the nephridiopore into the mantle cavity. Octopuses (along with cuttlefish ) have the highest brain-to-body mass ratios of all invertebrates; this is greater than that of many vertebrates. Octopuses have the same jumping genes that are active in the human brain, implying an evolutionary convergence at molecular level. The nervous system

15540-470: The respiratory chamber. The lamella structure of the gills allows for a high oxygen uptake, up to 65% in water at 20 °C (68 °F). Water flow over the gills correlates with locomotion, and an octopus can propel its body when it expels water out of its siphon. The thin skin of the octopus absorbs additional oxygen. When resting, around 41% of an octopus's oxygen absorption is through the skin. This decreases to 33% when it swims, as more water flows over

15680-427: The rocks and feels through the crevices. The creature may make a jet-propelled pounce on prey and pull it toward the mouth with its arms, the suckers restraining it. Small prey may be completely trapped by the webbed structure. Octopuses usually inject crustaceans like crabs with a paralysing saliva then dismember them with their beaks. Octopuses feed on shelled molluscs either by forcing the valves apart, or by drilling

15820-613: The seafloor and metamorphoses into the adult form. While metamorphosis is the usual state in molluscs, the cephalopods differ in exhibiting direct development: the hatchling is a 'miniaturized' form of the adult. The development of molluscs is of particular interest in the field of ocean acidification as environmental stress is recognized to affect the settlement, metamorphosis, and survival of larvae. Most molluscs are herbivorous, grazing on algae or filter feeders. For those grazing, two feeding strategies are predominant. Some feed on microscopic, filamentous algae, often using their radula as

15960-403: The sensors recognise octopus skin and prevent self-attachment. Octopuses appear to have poor proprioceptive sense and must observe the arms visually to keep track of their position. The ink sac of an octopus is located under the digestive gland. A gland attached to the sac produces the ink , and the sac stores it. The sac is close enough to the funnel for the octopus to shoot out the ink with

16100-461: The skin respond to different wavelengths of light and help the animals choose a colouration that camouflages them; the chromatophores in the skin can respond to light independently of the eyes. An alternative hypothesis is that cephalopod eyes in species that only have a single photoreceptor protein may use chromatic aberration to turn monochromatic vision into colour vision, though this sacrifices image quality. This would explain pupils shaped like

16240-415: The smaller particles, mainly minerals, to the prostyle so eventually they are excreted, while the larger ones, mainly food, are sent to the stomach's cecum (a pouch with no other exit) to be digested. The sorting process is by no means perfect. Periodically, circular muscles at the hindgut's entrance pinch off and excrete a piece of the prostyle, preventing the prostyle from growing too large. The anus, in

16380-477: The species and water temperature. They feed on copepods , arthropod larvae and other zooplankton , eventually settling on the ocean floor and developing directly into adults with no distinct metamorphoses that are present in other groups of mollusc larvae. Octopus species that produce larger eggs – including the southern blue-ringed , Caribbean reef , California two-spot , Eledone moschata and deep sea octopuses – instead hatch as benthic animals similar to

16520-421: The sperm from the spermatophore, and it is stored internally by the female. About forty days after mating, the female giant Pacific octopus attaches strings of small fertilised eggs (10,000 to 70,000 in total) to rocks in a crevice or under an overhang. Here she guards and cares for them for about five months (160 days) until they hatch. In colder waters, such as those off Alaska , it may take up to ten months for

16660-412: The stomach and projecting slightly into the hindgut is the prostyle, a backward-pointing cone of feces and mucus, which is rotated by further cilia so it acts as a bobbin, winding the mucus string onto itself. Before the mucus string reaches the prostyle, the acidity of the stomach makes the mucus less sticky and frees particles from it. The particles are sorted by yet another group of cilia, which send

16800-435: The subject of molluscan anatomy by describing what is called an archi-mollusc , hypothetical generalized mollusc , or hypothetical ancestral mollusc ( HAM ) to illustrate the most common features found within the phylum. The depiction is visually rather similar to modern monoplacophorans . The generalized mollusc is an unsegmented, bilaterally symmetrical animal and has a single, " limpet -like" shell on top. The shell

16940-419: The suckers adhere to the substrate and the animal hauls itself forward with its powerful arm muscles, while other arms may push rather than pull. As progress is made, other arms move ahead to repeat these actions and the original suckers detach. During crawling, the heart rate nearly doubles, and the animal requires ten or fifteen minutes to recover from relatively minor exercise. Most octopuses swim by expelling

17080-420: The surrounding water. Mollusca Mollusca is a phylum of protostomic invertebrate animals , whose members are known as molluscs or mollusks ( / ˈ m ɒ l ə s k s / ). Around 76,000  extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda . The number of additional fossil species is estimated between 60,000 and 100,000, and

17220-499: The three functioning as the principal center of "thinking". Some such as the scallops have eyes around the edges of their shells which connect to a pair of looped nerves and which provide the ability to distinguish between light and shadow. The simplest molluscan reproductive system relies on external fertilization , but with more complex variations. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults. Two gonads sit next to

17360-414: The timing of reproduction and lifespan. When octopuses reproduce, the male uses a specialised 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, which has a spoon-shaped depression and modified suckers near

17500-492: The tip. In most species, fertilisation occurs in the mantle cavity. The reproduction of octopuses has been studied in only a few species. One such species is the giant Pacific octopus , in which courtship is accompanied, especially in the male, by changes in skin texture and colour. 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

17640-423: The total number of mollusc species ever to have existed, whether or not preserved, must be many times greater than the number alive today. Molluscs have more varied forms than any other animal phylum . They include snails , slugs and other gastropods ; clams and other bivalves ; squids and other cephalopods ; and other lesser-known but similarly distinctive subgroups. The majority of species still live in

17780-403: The two largest species of octopus, usually lives for three to five years. Octopus lifespan is limited by reproduction. For most octopuses, the last stage of their life is called senescence. It is the breakdown of cellular function without repair or replacement. For males, this typically begins after mating. Senescence may last from weeks to a few months, at most. For females, it begins when they lay

17920-809: The two phonemes in all varieties, but the pronunciation is not differentiated in Latin American varieties, some speakers also get mixed up with the spelling. Many Spanish dialects tend to aspirate syllable-final /s/ , and some even elide it often. Since this phenomenon is somewhat stigmatized, some speakers in the Caribbean and especially the Dominican Republic may attempt to correct for it by pronouncing an /s/ where it does not belong. For example, catorce años '14 years' may be pronounced as catorces año . The East Franconian dialects are notable for lenition of stops /p/ /t/ /k/ to [b], [d], [g]. Thus,

18060-492: The typical octopus body shape. Basal species, the Cirrina , have stout gelatinous bodies with webbing that reaches near the tip of their arms, and two large fins above the eyes, supported by an internal shell . Fleshy papillae or cirri are found along the bottom of the arms, and the eyes are more developed. Octopuses have a closed circulatory system , in which the blood remains inside blood vessels. Octopuses have three hearts;

18200-402: The urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity. Exceptions to the above are the molluscs Planorbidae or ram's horn snails, which are air-breathing snails that use iron-based hemoglobin instead of the copper-based hemocyanin to carry oxygen through their blood. Most molluscs have only one pair of gills, or even only

18340-520: The usual fashion, but its diet includes protists such as the xenophyophore Stannophyllum . Sacoglossan sea-slugs suck the sap from algae, using their one-row radula to pierce the cell walls, whereas dorid nudibranchs and some Vetigastropoda feed on sponges and others feed on hydroids . (An extensive list of molluscs with unusual feeding habits is available in the appendix of GRAHAM, A. (1955). "Molluscan diets" . Journal of Molluscan Studies . 31 (3–4): 144. .) Opinions vary about

18480-405: The visceral hump leads, the siphon points at the head and the arms trail behind, with the animal presenting a fusiform appearance. In an alternative method of swimming, some species flatten themselves dorso-ventrally, and swim with the arms held out sideways; this may provide lift and be faster than normal swimming. Jetting is used to escape from danger, but is physiologically inefficient, requiring

18620-421: The vital organs. The mantle cavity has muscular walls and contains the gills; it is connected to the exterior by a funnel or siphon . The mouth of an octopus, located underneath the arms, has a sharp hard beak . The skin consists of a thin outer epidermis with mucous cells and sensory cells and a connective tissue dermis consisting largely of collagen fibres and various cells allowing colour change. Most of

18760-417: The water over their gills. Most bivalves are filter feeders, which can be measured through clearance rates. Research has demonstrated that environmental stress can affect the feeding of bivalves by altering the energy budget of organisms. Cephalopods are primarily predatory, and the radula takes a secondary role to the jaws and tentacles in food acquisition. The monoplacophoran Neopilina uses its radula in

18900-402: The word escape by writing or saying scape , or for the word establish by writing or saying stablish , which is archaic , or an informal pronunciation in some dialects. As the locative case is rarely found in vernacular usage in the southern and eastern dialects of Serbia, and the accusative is used instead, speakers tend to overcorrect when trying to deploy the standard variety of

19040-516: The yolk, forming a yolk sac, which eventually forms part of the gut. The dorsal side of the disc grows upward and forms the embryo, with a shell gland on its dorsal surface, gills, mantle and eyes. The arms and funnel develop as part of the foot on the ventral side of the disc. The arms later migrate upward, coming to form a ring around the funnel and mouth. The yolk is gradually absorbed as the embryo develops. Most young octopuses hatch as paralarvae and are planktonic for weeks to months, depending on

19180-698: The young octopuses hatch. In laboratory experiments, octopuses can readily be trained to distinguish between different shapes and patterns. They have been reported to practise observational learning , although the validity of these findings is contested. Octopuses have also been observed in what has been 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. Growing evidence suggests that octopuses are sentient and capable of experiencing pain . The veined octopus collects discarded coconut shells, then uses them to build

19320-411: Was an animal with a live mass of 71 kg (157 lb). Much larger sizes have been claimed for the giant Pacific octopus: one specimen was recorded as 272 kg (600 lb) with an arm span of 9 m (30 ft). A carcass of the seven-arm octopus , Haliphron atlanticus , weighed 61 kg (134 lb) and was estimated to have had a live mass of 75 kg (165 lb). The smallest species

19460-437: Was at the rear in the earliest molluscs, but its position now varies from group to group. The anus , a pair of osphradia (chemical sensors) in the incoming "lane", the hindmost pair of gills and the exit openings of the nephridia (kidneys) known as "Organs of bojanus" and gonads (reproductive organs) are in the mantle cavity. The whole soft body of bivalves lies within an enlarged mantle cavity. The mantle edge secretes

19600-582: Was based on a real person the creators encountered at a restaurant in Cookham . The same, for the same reason, is often heard when a person of Italian origins speaks English: "I'm h angry h at Francesco", "I'd like to h eat something". This should not be expected to be consistent with the h-dropping common in the Italian accent, so the same person may say "an edge-og" instead of "a hedgehog" or just say it correctly. Hyperforeignism arises from speakers misidentifying

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