Squid are cephalopods in the superorder Decapodiformes with elongated bodies, large eyes, eight arms and two tentacles. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.

Squid diverged from other cephalopods during the Jurassic and occupy a similar role to teleost fish as open water predators of similar size and behaviour. They play an important role in the open water food web. The two long tentacles are used to grab prey and the eight arms to hold and control it. The beak then cuts the food into suitable size chunks for swallowing. Squid are rapid swimmers, moving by jet propulsion, and largely locate their prey by sight. They are among the most intelligent of invertebrates, with groups of Humboldt squid having been observed hunting cooperatively. They are preyed on by sharks, other fish, sea birds, seals and cetaceans, particularly sperm whales.

Squid can change colour for camouflage and signalling. Some species are bioluminescent, using their light for counter-illumination camouflage, while many species can eject a cloud of ink to distract predators.

Squid are used for human consumption with commercial fisheries in Japan, the Mediterranean, the southwestern Atlantic, the eastern Pacific and elsewhere. They are used in cuisines around the world, often known as "calamari". Squid have featured in literature since classical times, especially in tales of giant squid and sea monsters.

Temporal range: Early Devonian – Recent[1]
Caribbean reef squid ("Sepioteuthis sepioidea")
Caribbean reef squid (Sepioteuthis sepioidea)
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
(unranked): Neocoleoidea
Superorder: Decapodiformes
Leach, 1817[2]

Taxonomy and phylogeny

Squid are members of the class Cephalopoda, subclass Coleoidea. The squid orders Myopsida and Oegopsida are in the superorder Decapodiformes (from the Greek for "ten-legged"). Two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from squids and differ recognizably in their gross anatomical features. They are the bobtail squid of order Sepiolida and the ram's horn squid of the monotypic order Spirulida. The vampire squid, however, is more closely related to the octopuses than to any squid.[4]

The cladogram, not fully resolved, is based on Sanchez et al, 2018. Their molecular phylogeny used mitochondrial and nuclear DNA marker sequences; they comment that a robust phylogeny "has proven very challenging to obtain". If it is accepted that Sepiidae cuttlefish are a kind of squid, then the squids, excluding the vampire squid, form a clade as illustrated.[4] Orders are shown in boldface; all the families not included in those orders are in the paraphyletic order "Oegopsida".


Nautilus Nautilus Palau.JPG

Octopuses and allies

Octopoda, Argonautoidea, and Cirrina Papierboot Argonauta 200705181139.jpg

Vampyroteuthidae (vampire squid) Vampire des abysses.jpg


Cranchiinae (glass squid A) Cranchiidae sp (cropped).jpg


Psychroteuthidae (glacial squid) Psychroteuthis glacialis paralarva

Onychoteuthidae (hooked squid) Onychoteuthis banksii2

Taoniinae (glass squid B)

Architeuthidae (giant squid) Architeuthis princeps image modified

Lepidoteuthidae (Grimaldi scaled squid) Lepidoteuthis grimaldii 617 mm ML

Octopoteuthidae (octopus squid) Taningia danae

Ancistrocheiridae (sharpear enope squid) Ancistrocheirus lesueurii

Lycoteuthidae (firefly squid) Lycoteuthis lorigera male

Pyroteuthidae (fire squid) Pyroteuthismargaritifera

Bathyteuthidae Bathyteuthisabyssicola (top)

Ommastrephidae (flying squid) Lesser Flying Squid - Todaropsis eblanae.jpg

Pholidoteuthidae Pholidoteuthis massyae (cropped)

Gonatidae (armhook squid) Berryteuthis magister.jpg

Chiroteuthidae (whip-lash squid[a]) Chiroteuthid

Sepiolida (bobtail squid) Austrorossia mastigophora (rotated)

Sepiadariidae (pyjama and bottletail squid) Striped pyjama squid

Chtenopterygidae Chtenopteryx sicula 1 (rotated)

Thysanoteuthidae Thysanoteuthis rhombus

Enoploteuthidae Mollusques méditeranéens (Abralia veranyi)

Brachioteuthidae Brachioteuthis riisei1


Histioteuthidae (cock-eyed squid) Histioteuthidae - Histioteuthis bonnellii

Batoteuthidae (bush-club squid)

Mastigoteuthidae (whip-lash squid) Mastigoteuthis agassizii1

Joubiniteuthidae (Joubin's squid) Joubiniteuthis portieri.jpg

Magnapinnidae (bigfin squid) Magnapinna talismani.jpg

Spirulida (ram's horn squid) Spirula spirula illustration.jpg

Myopsida (neritic squid) Loliginidae Loligo vulgaris1

Sepiidae (cuttlefish) Sepia officinalis1

Idiosepiidae (pygmy squid)


Crown coleoids (the ancestors of octopuses and squid) diverged at the end of the Paleozoic, in the Permian. Squid diverged during the Jurassic, but many squid families appeared in or after the Cretaceous.[5] Both the coleoids and the teleost fish were involved in much adaptive radiation at this time, and the two modern groups resemble each other in size, ecology, habitat, morphology and behaviour, however some fish moved into fresh water while the coleoids remained in marine environments.[6]

The ancestral coleoid was probably nautiloid-like with a strait septate shell that became immersed in the mantle and was used for buoyancy control. Four lines diverged from this, Spirulida (with one living member), the cuttlefishes, the squids and the octopuses. Squid have differentiated from the ancestral mollusc such that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What may have been the foot of the ancestor is modified into a complex set of appendages around the mouth. The sense organs are highly developed and include advanced eyes similar to those of vertebrates.[6]

The ancestral shell has been lost, with only an internal gladius, or pen, remaining. The pen, made of a chitin-like material,[6][7] is a feather-shaped internal structure that supports the squid's mantle and serves as a site for muscle attachment. The cuttlebone or sepion of the Sepiidae is calcareous and appears to have evolved afresh in the Tertiary.[8]

Rhomboteuthis lehmani (cropped)

Fossil Rhomboteuthis from the Lower Callovian (c. 164 mya, middle Jurassic) of La Voulte-sur-Rhône, France

Plesioteuthis prisca 01

Fossil Plesioteuthis from the Tithonian (c. 150 mya, upper Jurassic), Solnhofen, Germany


Composite diagram illustrating basic squid features, ventral aspect
Basic squid features (ventral aspect)

Squid are soft-bodied molluscs whose forms have been modified to adopt an active predatory lifestyle. The head and foot of the squid are at one end of a long body, and this end is functionally anterior, leading the animal as it moves through the water. The foot has been transformed into a set of eight arms and two distinctive tentacles, which surround the mouth; each appendage takes the form of a muscular hydrostat and is flexible and prehensile, usually bearing disc-like suckers.[6]

The suckers may lie directly on the arm or be stalked. Their rims are stiffened with chitin and may contain minute toothlike denticles. These features, as well as strong musculature, and a small ganglion beneath each sucker to allow individual control, provide a very powerful adhesion to grip prey. Hooks are present on the arms and tentacles in some species, but their function is unclear.[9] The two tentacles are much longer than the arms and are retractile. Suckers are limited to the spatulate tip of the tentacle, known as the manus.[6]

In the mature male, the outer half of one of the left arms is hectocotylised – and ends in a copulatory pad rather than suckers. This is used for depositing a spermatophore inside the mantle cavity of a female. A ventral part of the foot has been converted into a funnel through which water exits the mantle cavity.[6]

The main body mass is enclosed in the mantle, which has a swimming fin along each side. These fins are not the main source of locomotion in most species. The mantle wall is heavily muscled and internal. The visceral mass, which is covered by a thin, membranous epidermis, forms a cone-shaped posterior region known as the "visceral hump". The mollusc shell is reduced to an internal, longitudinal chitinous "pen" in the functionally dorsal part of the animal; the pen acts to stiffen the squid and provides attachments for muscles.[6]

On the functionally ventral part of the body is an opening to the mantle cavity, which contains the gills (ctenidia) and openings from the excretory, digestive and reproductive systems. An inhalant siphon behind the funnel draws water into the mantel cavity via a valve. The squid uses the funnel for locomotion via precise jet propulsion.[10] In this form of locomotion, water is sucked into the mantle cavity and expelled out of the funnel in a fast, strong jet. The direction of travel is varied by the orientation of the funnel.[6] Squid are strong swimmers and certain species can "fly" for short distances out of the water.[11]


Squid make use of different kinds of camouflage, namely active camouflage for background matching (in shallow water) and counter-illumination. This helps to protect them from their predators and allows them to approach their prey.[12][13]

The skin is covered in controllable chromatophores of different colours, enabling the squid to match its coloration to its surroundings.[12][14] The play of colours may in addition distract prey from the squid's approaching tentacles.[15] The skin also contains light reflectors called iridophores and leucophores that, when activated, in milliseconds create changeable skin patterns of polarized light.[16][17] Such skin camouflage may serve various functions, such as communication with nearby squid, prey detection, navigation, and orientation during hunting or seeking shelter.[16] Neural control of the iridophores enabling rapid changes in skin iridescence appears to be regulated by a cholinergic process affecting reflectin proteins.[17]

Some mesopelagic squid such as the firefly squid (Watasenia scintillans) and the midwater squid (Abralia veranyi) use counter-illumination camouflage, generating light to match the downwelling light from the ocean surface.[13][18][19] This creates the effect of countershading, making the underside lighter than the upperside.[13]

Counter-illumination is also used by the Hawaiian bobtail squid (Euprymna scolopes), which has symbiotic bacteria (Aliivibrio fischeri) that produce light to help the squid avoid nocturnal predators.[20] This light shines through the squid's skin on its underside and is generated by a large and complex two-lobed light organ inside the squid's mantle cavity. From there, it escapes downwards, some of it travelling directly, some coming off a reflector at the top of the organ (dorsal side). Below there is a kind of iris, which has branches (diverticula) of its ink sac, with a lens below that; both the reflector and lens are derived from mesoderm. The squid controls light production by changing the shape of its iris or adjusting the strength of yellow filters on its underside, which presumably change the balance of wavelengths emitted.[18] Light production shows a correlation with intensity of down-welling light, but it is about one third as bright; the squid can track repeated changes in brightness. Because the Hawaiian bobtail squid hides in sand during the day to avoid predators, it does not use counter-illumination during daylight hours.[18]


Controllable chromatophores of different colours in the skin of a squid allow it to change its coloration and patterns rapidly, whether for camouflage or signalling.

Squid Counterillumination

Principle of counter-illumination camouflage of the firefly squid, Watasenia scintillans. When seen from below by a predator, the animal's light helps to match its brightness and colour to the sea surface above.

Predator distraction with ink

Loligosepia aalensis 01
Fossil Loligosepia aalensis from the lower Jurassic; the ink sac is still full of black eumelanin pigment.

Squid distract attacking predators by ejecting a cloud of ink, giving themselves an opportunity to escape.[21][22] The ink gland and its associated ink sac empties into the rectum close to the anus, allowing the squid to rapidly discharge black ink into the mantle cavity and surrounding water.[9] The ink is a suspension of melanin particles and quickly disperses to form a dark cloud that obscures the escape manoeuvres of the squid. Predatory fish may also be deterred by the alkaloid nature of the discharge which may interfere with their chemoreceptors.[6]

Nervous system and sense organs

Cephalopods have the most highly developed nervous systems among invertebrates. Squids have a complex brain in the form of a nerve ring encircling the oesophagus, enclosed in a cartilaginous cranium. Paired cerebral ganglia above the oesophagus receive sensory information from the eyes and statocysts, and further ganglia below control the muscles of the mouth, foot, mantle and viscera. Giant axons up to 1 mm (0.039 in) in diameter convey nerve messages with great rapidity to the circular muscles of the mantle wall, allowing a synchronous, powerful contraction and maximum speed in the jet propulsion system.[6]

The paired eyes, on either side of the head, are housed in capsules fused to the cranium. Their structure is very similar to that of a fish eye, with a globular lens that has a depth of focus from 3 cm (1 in) to infinity. The image is focused by changing the position of the lens, as in a camera or telescope, rather than changing the shape of the lens, as in the human eye. Squid adjust to changes in light intensity by expanding and contracting the slit-shaped pupil.[6] Deep sea squids in the Histioteuthidae family have eyes of two different types and orientation. The large left eye is tubular in shape and looks upwards, presumably searching for the silhouettes of animals higher in the water column. The normally-shaped right eye points forwards and downwards to detect prey.[23]

The statocysts are involved in maintaining balance and are analogous to the inner ear of fish. They are housed in cartilaginous capsules on either side of the cranium. They provide the squid with information on its body position in relation to gravity, its orientation, acceleration and rotation, and are able to perceive incoming vibrations. Without the statocysts, the squid cannot maintain equilibrium.[6] Squid appear to have limited hearing,[24] but the head and arms bear lines of hair-cells that are weakly sensitive to water movements and changes in pressure, and are analogous in function to the lateral line system of fish.[6]

Reproductive system

Onykia ingens with erect penis
Male Onykia ingens with penis erected to 67 cm (26 in)

The sexes are separate in squid, there being a single gonad in the posterior part of the body with fertilisation being external, and usually taking place in the mantle cavity of the female. The male has a testis from which sperm pass into a single gonoduct where they are rolled together into a long bundle, or spermatophore. The gonoduct is elongated into a "penis" that extends into the mantle cavity and through which spermatophores are ejected. In shallow water species, the penis is short, and the spermatophore is removed from the mantle cavity by a tentacle of the male, which is specially adapted for the purpose and known as a hectocotylus, and placed inside the mantle cavity of the female during mating.[6]

Uroteuthis duvauceli hectocotylus
Hectocotylus of Uroteuthis duvauceli: one tentacle of the male is adapted for transferring the spermatophore.

The female has a large translucent ovary, situated towards the posterior of the visceral mass. From here, eggs travel along the gonocoel, where there are a pair of white nidamental glands, which lie anterior to the gills. Also present are red-spotted accessory nidamental glands containing symbiotic bacteria; both organs are associated with nutrient manufacture and forming shells for the eggs. The gonocoel enters the mantle cavity at the gonopore, and in some species, receptacles for storing spermatophores are located nearby, in the mantle wall.[6]

In shallow-water species of the continental shelf and epipelagic or mesopelagic zones, it is frequently one or both of arm pair IV of males that are modified into hectocotyli.[25] However, most deep-sea squid lack hectocotyl arms and have longer penises; Ancistrocheiridae and Cranchiinae are exceptions.[26] Giant squid of the genus Architeuthis are unusual in that they possess both a large penis and modified arm tips, although whether the latter are used for spermatophore transfer is uncertain.[26] Penis elongation has been observed in the deep-water species Onykia ingens; when erect, the penis may be as long as the mantle, head, and arms combined.[26][27] As such, deep-water squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile barnacles.[26]

Digestive system

Chtenopteryx sicula2 - from Commons
Ventral view of the viscera of a female Chtenopteryx sicula

Like all cephalopods, squids are predators and have complex digestive systems. The mouth is equipped with a sharp, horny beak mainly made of chitin and cross-linked proteins,[28] which is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain minerals, unlike the teeth and jaws of many other organisms; the cross-linked proteins are histidine- and glycine-rich and give the beak a stiffness and hardness greater than most equivalent synthetic organic materials.[29] The stomachs of captured whales often have indigestible squid beaks inside. The mouth contains the radula, the rough tongue common to all molluscs except bivalvia, which is equipped with multiple rows of teeth.[6] In some species, toxic saliva helps to control large prey; when subdued, the food can be torn in pieces by the beak, moved to the oesophagus by the radula, and swallowed.[30]

The food bolus is moved along the gut by waves of muscular contractions (peristalsis). The long oesophagus leads to a muscular stomach roughly in the middle of the visceral mass. The digestive gland, which is equivalent to a vertebrate liver, diverticulates here, as does the pancreas, and both of these empty into the caecum, a pouch-shaped sac where most of the absorption of nutrients takes place.[6] Indigestible food can be passed directly from the stomach to the rectum where it joins the flow from the caecum and is voided through the anus into the mantle cavity.[6] Cephalopods are short-lived, and in mature squid, priority is given to reproduction;[31] the female Onychoteuthis banksii for example, sheds its feeding tentacles on reaching maturity, and becomes flaccid and weak after spawning.[32][33]

Cardiovascular and excretory systems

The squid mantle cavity is a seawater-filled sac containing three hearts and other organs supporting circulation, respiration, and excretion.[34] Squid have a main systemic heart that pumps blood around the body as part of the general circulatory system, and two branchial hearts. The systemic heart consists of three chambers, a lower ventricle and two upper atria, all of which can contract to propel the blood. The branchial hearts pump blood specifically to the gills for oxygenation, before returning it to the systemic heart.[34] The blood contains the copper-rich protein hemocyanin, which is used for oxygen transport at low ocean temperatures and low oxygen concentrations, and makes the oxygenated blood a deep, blue color.[34] As systemic blood returns via two vena cavae to the branchial hearts, excretion of urine, carbon dioxide, and waste solutes occurs through outpockets (called nephridial appendages) in the vena cavae walls that enable gas exchange and excretion via the mantle cavity seawater.[34]


Cranchiidae sp
The body of glass squids (Cranchiidae) is mainly filled by a transparent coelom containing ammonium ions for buoyancy.

Unlike nautiloids which have gas-filled chambers inside their shells which provide buoyancy, and octopuses which live near and rest on the seabed and do not require to be buoyant, many squid have a fluid-filled receptacle, equivalent to the swim bladder of a fish, in the coelom or connective tissue. This reservoir acts as a chemical buoyancy chamber, with the heavy metallic cations typical of seawater replaced by low molecular-weight ammonium ions, a product of excretion. The small difference in density provides a small contribution to buoyancy per unit volume, so the mechanism requires a large buoyancy chamber to be effective. Since the chamber is filled with liquid, it has the advantage over a swim bladder of not changing significantly in volume with pressure. Glass squids in the family Cranchiidae for example, have an enormous transparent coelom containing ammonium ions and occupying about two-thirds the volume of the animal, allowing it to float at the required depth. About half of the 28 families of squid use this mechanism to solve their buoyancy issues.[6]

Largest and smallest

Giant Squid NASA
A giant squid. The bars are a metre (3 feet) apart.

The majority of squid are no more than 60 cm (24 in) long, although the giant squid may reach 13 m (43 ft).[35] The smallest species are probably the benthic pygmy squids Idiosepius, which grow to a mantle length of 10 to 18 mm (0.4 to 0.7 in), and have short bodies and stubby arms.[36]

In 1978, sharp, curved claws on the suction cups of squid tentacles cut up the rubber coating on the hull of the USS Stein. The size suggested the largest squid known at the time.[37]

In 2003, a large specimen of an abundant[38] but poorly understood species, Mesonychoteuthis hamiltoni (the colossal squid), was discovered. This species may grow to 10 m (33 ft) in length, making it the largest invertebrate.[39] In February 2007, a New Zealand fishing vessel caught the largest squid ever documented, weighing 495 kg (1,091 lb) and measuring around 10 m (33 ft) off the coast of Antarctica.[40] Dissection showed that the eyes, used to detect prey in the deep Southern Ocean, exceeded the size of footballs; these may be among the largest eyes ever to exist in the animal kingdom.[41]


The eggs of squid are large for a mollusc, containing a large amount of yolk to nourish the embryo as it develops directly, without an intervening veliger larval stage. The embryo grows as a disc of cells on top of the yolk. During the gastrulation stage, the margins of the disc grow to surround the yolk, forming a yolk sac, which eventually forms part of the animal's gut. The dorsal side of the disc grows upwards 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 upwards, coming to form a ring around the funnel and mouth. The yolk is gradually absorbed as the embryo grows. Some juvenile squid live higher in the water column than do adults. Squids tend to be short-lived; Loligo for example lives from one to three years according to species, typically dying soon after spawning.[6]

Bobtail Squid Light Organ
Sagittal section of the large eye-like light-producing organ of Hawaiian bobtail squid, Euprymna scolopes. The organ houses symbiotic Aliivibrio fischeri bacteria.

In a well-studied bioluminescent species, the Hawaiian bobtail squid, a special light organ in the squid's mantle is rapidly colonized with Aliivibrio fischeri bacteria within hours of hatching. This light-organ colonization requires this particular bacterial species for a symbiotic relationship; no colonization occurs in the absence of A. fischeri.[20] Colonization occurs in a horizontal manner, such that the hosts acquires its bacterial partners from the environment. The symbiosis is obligate for the squid, but facultative for the bacteria. Once the bacteria enter the squid, they colonize interior epithelial cells in the light organ, living in crypts with complex microvilli protrusions. The bacteria also interact with hemocytes, macrophage-like blood cells that migrate between epithelial cells, but the mechanism and function of this process is not well understood. Bioluminescence reaches its highest levels during the early evening hours and bottoms out before dawn; this occurs because at the end of each day, the contents of the squid's crypts are expelled into the surrounding environment.[42] About 95% of the bacteria are voided each morning before the bacterial population builds up again by nightfall.[18]



Euprymna scolopes - image.pbio.v12.i02.g001
Hawaiian bobtail squid swimming slowly by undulating its fins

Squid can move about in several different ways. Slow movement is achieved by a gentle undulation of the muscular lateral fins on either side of the trunk which drives the animal forward. A more common means of locomotion providing sustained movement is achieved using jetting, during which contraction of the muscular wall of the mantle cavity provides jet propulsion.[6]

Slow jetting is used for ordinary locomotion, and ventilation of the gills is achieved at the same time. The circular muscles in the mantle wall contract; this causes the inhalant valve to close, the exhalant valve to open and the mantle edge to lock tightly around the head. Water is forced out through the funnel which is pointed in the opposite direction to the required direction of travel. The inhalant phase is initiated by the relaxation of the circular muscles causes them to stretch, the connective tissue in the mantle wall recoils elastically, the mantle cavity expands causing the inhalant valve to open, the exhalant valve to close and water to flow into the cavity. This cycle of exhalation and inhalation is repeated to provide continuous locomotion.[6]

Fast jetting is an escape response. In this form of locomotion, radial muscles in the mantle wall are involved as well as circular ones, making it possible to hyper-inflate the mantle cavity with a larger volume of water than during slow jetting. On contraction, water flows out with great force, the funnel always being pointed anteriorly, and travel is backwards. During this means of locomotion, some squid exit the water in a similar way to flying fish, gliding through the air for up to 50 m (160 ft), and occasionally ending up on the decks of ships.[6]


Squid are carnivores, and, with their strong arms and suckers, can overwhelm relatively large animals efficiently. Prey is identified by sight or by touch, grabbed by the tentacles which can be shot out with great rapidity, brought back to within reach of the arms, and held by the hooks and suckers on their surface.[43] In some species, the squid's saliva contains toxins which act to subdue the prey. These are injected into its bloodstream when the prey is bitten, along with vasodilators and chemicals to stimulate the heart, and quickly circulate to all parts of its body.[6] The deep sea squid Taningia danae has been filmed releasing blinding flashes of light from large photophores on its arms to illuminate and disorientate potential prey.[44]

Ventouse calmar
The whip-like tentacles of Mastigoteuthis are covered with tiny suckers to catch small organisms like flypaper.

Although squid can catch large prey, the mouth is relatively small, and the food must be cut into pieces by the chitinous beak with its powerful muscles before being swallowed. The radula is located in the buccal cavity and has multiple rows of tiny teeth that draw the food backwards and grind it in pieces.[6] The deep sea squid Mastigoteuthis has the whole length of its whip-like tentacles covered with tiny suckers; it probably catches small organisms in the same way that flypaper traps flies. The tentacles of some bathypelagic squids bear photophores which may bring food within its reach by attracting prey.[43]

Squid are among the most intelligent invertebrates. For example, groups of Humboldt squid hunt cooperatively, spiralling up through the water at night and coordinating their vertical and horizontal movements while foraging.[45]


Squid colors 2
The Caribbean reef squid (Sepioteuthis sepioidea) employs a complex array of colour changes during courtship and social interactions.

Courtship in squid takes place in the open water and involves the male selecting a female, the female responding, and the transfer by the male of spermatophores to the female. In many instances, the male may display to identify himself to the female and drive off any potential competitors.[46] Elaborate changes in body patterning take place in some species in both agonistic and courtship behaviour. The Caribbean reef squid (Sepioteuthis sepioidea), for example, employs a complex array of colour changes during courtship and social interactions and has a range of about 16 body patterns in its repertoire.[47]

The pair adopt a head-to-head position, and "jaw locking" may take place, in a similar manner to that adopted by some cichlid fish.[48] The heterodactylus of the male is used to transfer the spermatophore and deposit it in the female's mantle cavity in the position appropriate for the species; this may be adjacent to the gonopore or in a seminal receptacle.[6]

Squid Eggs (6997601241)
Squid eggs

The sperm may be used immediately or may be stored. As the eggs pass down the oviduct, they are wrapped in a gelatinous coating, before continuing to the mantle cavity, where they are fertilised. In Loligo, further coatings are added by the nidimental glands in the walls of the cavity and the eggs leave through a funnel formed by the arms. The female attaches them to the substrate in strings or groups, the coating layers swelling and hardening after contact with sea water. Loligo sometimes forms breeding aggregations which may create a "community pile" of egg strings. Some pelagic and deep sea squid do not attach their egg masses, which float freely.[6]


Squid mostly have an annual life cycle, growing fast and dying soon after spawning. The diet changes as they grow but mostly consists of large zooplankton and small nekton. In Antarctica for example, krill is the main constituent of the diet, with other food items being amphipods, other small crustaceans, and large arrow worms. Fish are also eaten, and some squid are cannibalistic.[49]

As well as occupying a key role in the food chain, squid are an important prey for predators including sharks, sea birds, seals and whales. Juvenile squid provide part of the diet for worms and small fish. When researchers studied the contents of the stomachs of elephant seals in South Georgia, they found 96% squid by weight.[50] In a single day, a sperm whale can eat 700 to 800 squid,[50] and a Risso's dolphin entangled in a net in the Mediterranean was found to have eaten angel clubhook squid, umbrella squid, reverse jewel squid and European flying squid, all identifiable from their indigestible beaks.[51] Ornithoteuthis volatilis, a common squid from the tropical Indo-Pacific, is predated by yellowfin tuna, longnose lancetfish, common dolphinfish and swordfish, the tiger shark, the scalloped hammerhead shark and the smooth hammerhead shark. Sperm whales also hunt this species extensively as does the brown fur seal.[52] In the Southern Ocean, penguins and wandering albatrosses are major predators of Gonatus antarcticus.[53]

Human uses

In literature and art

Giant squid have featured as monsters of the deep since classical times. Giant squid were described by Aristotle (4th century BC) in his History of Animals[54] and Pliny the Elder (1st century AD) in his Natural History.[55][56] The Gorgon of Greek mythology may have been inspired by squid or octopus, the animal itself representing the severed head of Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes.[57] The six-headed sea monster of the Odyssey, Scylla, may have had a similar origin. The Nordic legend of the kraken may also have derived from sightings of large cephalopods.[58]

In literature, H. G. Wells' short story "The Sea Raiders" featured a man-eating squid species Haploteuthis ferox.[59] The science fiction writer Jules Verne told a tale of a kraken-like monster in his 1870 novel Twenty Thousand Leagues Under the Sea.[58]

As food

Fried calamari
Fried calamari: breaded, deep-fried squid

Squid form a major food resource and are used in cuisines around the world, notably in Japan where it is eaten as ika-somen, sliced into vermicelli-like strips; as sashimi; and as tempura.[60] Three species of Loligo are used in large quantities, L. vulgaris in the Mediterranean (known as Calamar in Spanish, Calamaro in Italian); L. forbesii in the Northeast Atlantic; and L. pealei on the American East Coast.[60] Among the Ommastrephidae, Todarodes pacificus is the main commercial species, harvested in large quantities across the North Pacific in Canada, Japan and China.[60]

In English-speaking countries, squid as food is often called calamari, adopted from Italian into English in the 17th century.[61] Squid are found abundantly in certain areas, and provide large catches for fisheries. The body can be stuffed whole, cut into flat pieces, or sliced into rings. The arms, tentacles, and ink are also edible; the only parts not eaten are the beak and gladius (pen). Squid is a good food source for zinc and manganese, and high in copper,[62] selenium, vitamin B12, and riboflavin.[63]

Commercial fishing

According to the FAO, the cephalopod catch for 2002 was 3,173,272 tonnes (6.995867×109 lb). Of this, 2,189,206 tonnes, or 75.8 percent, was squid.[64] The following table lists squid species fishery catches that exceeded 10,000 tonnes (22,000,000 lb) in 2002.

World squid catch in 2002[64]
Species Family Common name Catch
Loligo gahi or Doryteuthis gahi Loliginidae Patagonian squid 24,976 1.1
Loligo pealei Loliginidae Longfin inshore squid 16,684 0.8
Common squid nei[b] Loliginidae 225,958 10.3
Ommastrephes bartramii Ommastrephidae Neon flying squid 22,483 1.0
Illex argentinus Ommastrephidae Argentine shortfin squid 511,087 23.3
Dosidicus gigas Ommastrephidae Humboldt squid 406,356 18.6
Todarodes pacificus Ommastrephidae Japanese flying squid 504,438 23.0
Nototodarus sloanii Ommastrephidae Wellington flying squid 62,234 2.8
Squid nei[b] Various 414,990 18.6
Total squid 2,189,206 100.0

In biomimicry

Smitt hysteresis graph
Schmitt trigger (B) mimicking the squid giant axon removes noise from noisy analog input (U), where ordinary comparator (A) does not. Green dashed lines are thresholds.

Prototype chromatophores that mimic the squid's adaptive camouflage, have been made by Bristol University researchers using an electroactive dielectric elastomer, a flexible "smart" material that changes its colour and texture in response to electrical signals. The researchers state that their goal is to create an artificial skin that provides rapid active camouflage.[65]

The squid giant axon inspired Otto Schmitt to develop a comparator circuit with hysteresis now called the Schmitt trigger, replicating the axon's propagation of nerve impulses.[66]

See also


  1. ^ Common name is however shared with Mastigoteuthidae.
  2. ^ a b Nei: not elsewhere included


  1. ^ see Boletzkyida, Belemnite
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External links


A cephalopod () is any member of the molluscan class Cephalopoda (Greek plural κεφαλόποδα, kephalópoda; "head-feet") such as a squid, octopus or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites).

Colossal squid

The colossal squid (Mesonychoteuthis hamiltoni, from Greek mesos (middle), onycho (claw, nail), and teuthis (squid)), sometimes called the Antarctic squid or giant cranch squid, is believed to be the largest squid species in terms of mass. It is the only known member of the genus Mesonychoteuthis. It is known from only a few specimens, and current estimates put its maximum size at 12–14 m (39–46 ft) long and weighing possibly up to 750 kilograms (1,650 lb), based on analysis of smaller and immature specimen, making it the largest-known invertebrate.

Dried shredded squid

Dried shredded squid is a dried, shredded, seasoned, seafood product, made from squid or cuttlefish, commonly found in coastal Asian countries, Russia, and Hawaii. The snack is also referred to as dried shredded cuttlefish.

Giant squid

The giant squid (genus Architeuthis) is a deep-ocean dwelling squid in the family Architeuthidae. Giant squid can grow to a tremendous size due to deep-sea gigantism: recent estimates put the maximum size at 13 m (43 ft) for females and 10 m (33 ft) for males from the posterior fins to the tip of the two long tentacles (second only to the colossal squid at an estimated 14 m (46 ft), one of the largest living organisms). The mantle is about 2 m (6 ft 7 in) long (more for females, less for males), and the length of the squid excluding its tentacles (but including head and arms) rarely exceeds 5 m (16 ft). Claims of specimens measuring 20 m (66 ft) or more have not been scientifically documented.

The number of different giant squid species has been debated, but recent genetic research suggests that only one species exists.In 2004, Japanese researchers took the first images of a live giant squid in its natural habitat, and in July 2012, a live adult was first filmed in its natural habitat off Chichijima.

Humboldt squid

The Humboldt squid (Dosidicus gigas), also known as jumbo squid, jumbo flying squid, pota, or diablo rojo (red devil), is a large, predatory squid living in the waters of the Humboldt Current in the eastern Pacific Ocean. It is the only species of the genus Dosidicus of the subfamily Ommastrephinae, family Ommastrephidae.

Humboldt squid typically reach a mantle length of 1.5 m (4 ft 11 in). They have a reputation for aggression towards humans, though this behavior may possibly only be manifested during feeding times. Like other members of the subfamily Ommastrephinae, they possess bioluminescent photophores and are capable of quickly changing body coloration (metachrosis). They notably rapidly flash red and white while hunting, earning them the name diablo rojo (Spanish for "red devil") among fishermen. These chromatophores (which belong to more than one set and are of different sizes) may rapidly cycle through colors other than red and white, flashing too quickly for the human eye to see the transitions. They have a relatively short lifespan of just 1-2 years.

They are most commonly found at depths of 200 to 700 m (660 to 2,300 ft), from Tierra del Fuego to California. This species is spreading north into the waters of Oregon, Washington, British Columbia, and Alaska. They are fished commercially, predominantly in Mexico and Peru.

The genus contains bioluminescent species.

Japanese flying squid

The Japanese flying squid, Japanese common squid or Pacific flying squid, scientific name Todarodes pacificus, is a squid of the family Ommastrephidae. This animal lives in the northern Pacific Ocean, in the area surrounding Japan, along the entire coast of China up to Russia, then spreading across the Bering Strait east towards the southern coast of Alaska and Canada. They tend to cluster around the central region of Vietnam.

Mantle (mollusc)

The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.

In many species of molluscs the epidermis of the mantle secretes calcium carbonate and conchiolin, and creates a shell. In sea slugs there is a progressive loss of the shell and the mantle becomes the dorsal surface of the animal.

The words mantle and pallium both originally meant cloak or cape, see mantle (vesture). This anatomical structure in molluscs often resembles a cloak because in many groups the edges of the mantle, usually referred to as the mantle margin, extend far beyond the main part of the body, forming flaps, double-layered structures which have been adapted for many different uses, including for example, the siphon.


Neocoleoidea is a large group of marine cephalopods. This cohort contains two extant groups: Decapodiformes (squid, cuttlefish, and relatives) and Octopodiformes (octopuses and the vampire squid). Species within this group exist in all major habitats in the ocean, in both the southern and northern polar regions, and from intertidal zones to great depths. Whilst conventionally held to be monophyletic, the only morphological character for the group is the presence of suckers: although the presence of these features in the belemnites suggests that they do not support the Neocoleoidea, and hence that the group may be paraphyletic.

Neon flying squid

The neon flying squid (Ommastrephes bartramii), sometimes called the red flying squid, akaika, and red squid is a species of large flying squid in the family Ommastrephidae. They are found in subtropical and temperate oceanic waters globally.The genus contains bioluminescent species.


Oegopsida is one of the two orders of squid in the superorder Decapodiformes, in the class Cephalopoda. Together with the Myopsina, it was formerly considered to be a suborder of the order Teuthida, in which case it was known as Oegopsina. This reclassification is due to Oegopsina and Myopsina not being demonstrated to form a clade.The Oegopsida are an often pelagic squid, with some nerito-oceanic species associated with sea mounts. They consist of 24 families and 69 genera. They have these characters in common: the head is without tentacle pockets, eyes lack a corneal covering, arms and tentacle clubs may have hooks, the buccal supports are without suckers, and oviducts in females are paired.

Two families, the Bathyteuthidae and Chtenopterygidae, which have features characteristic of the Myopsida while retaining others common to the Oegopsina, are sometimes placed in the Bathyteuthoidea.

The Oegopsida differ from the coastal Myopsida, characterised by the genus Loligo, which have corneal coverings over the eyes and tentacle pockets, but lack hooks, have no suckers on the buccal supports, and a single oviduct.

Oegopsid squid are the only decapods that lack a pocket for the tentacles. Otherwise, they share different characters with different decapod groups. Like the Bathyteuthoidea and Myopsida, the Oegopsida have a brachial canal, which is absent in other forms. As with the Spirulidae and Idiosepiidae, the Oegposida lack suckers on the buccal supports, and like the Bathyteuthoidea, Idiosepiidae, and Spirulidae, they have no circular muscle on the suckers.

Order Oegopsida

Family Ancistrocheiridae

Family Architeuthidae

Family Bathyteuthidae

Family Batoteuthidae

Family Brachioteuthidae

Family Chiroteuthidae

Family Chtenopterygidae

Family Cranchiidae

Family Cycloteuthidae

Family Enoploteuthidae

Family Gonatidae

Family Histioteuthidae

Family Joubiniteuthidae

Family Lepidoteuthidae

Family Lycoteuthidae

Family Magnapinnidae

Family Mastigoteuthidae

Family Neoteuthidae

Family Octopoteuthidae

Family Ommastrephidae

Family Onychoteuthidae

Family Pholidoteuthidae

Family Promachoteuthidae

Family Psychroteuthidae

Family Pyroteuthidae

Family Thysanoteuthidae

Parateuthis tunicata (incertae sedis)These families group into a number of different clades but these have not yet been formally given names. These groupings are:






































A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors. The bioluminescence can variously be produced from compounds during the digestion of prey, from specialized mitochondrial cells in the organism, called photocytes ("light producing" cells), or, similarly, associated with symbiotic bacteria in the organism that is cultured.

The character of photophores is important in the identification of deep sea fishes. Photophores on fish are used for attracting food or for camouflage from predators by counter-illumination.

Photophores are found on some cephalopods, including firefly squid, the sparkling enope or firefly squid, which can create impressive light displays.

Salted squid

Salted squid is squid or cuttlefish cured with dry salt and thus preserved for later consumption. Drying or salting, either with dry salt or with brine is a widely available method of seafood preservation. Salted squid is often mistaken with dried shredded squid, which is specifically shredded and seasoned dried squid. The salted squid production method is similar to salted fish and often considered as a specific variant of salted fish. Salted squid commonly found in coastal Asian countries, especially Indonesia, Malaysia, Thailand, Vietnam, Hong Kong, Southern China, South Korea and Japan.

Squid (software)

Squid is a caching and forwarding HTTP web proxy. It has a wide variety of uses, including speeding up a web server by caching repeated requests, caching web, DNS and other computer network lookups for a group of people sharing network resources, and aiding security by filtering traffic. Although primarily used for HTTP and FTP, Squid includes limited support for several other protocols including Internet Gopher, SSL, TLS and HTTPS. Squid does not support the SOCKS protocol.

Squid was originally designed to run as a daemon on Unix-like systems. A Windows port was maintained up to version 2.7. New versions available on Windows use the Cygwin environment. Squid is free software released under the GNU General Public License.

Squid (weapon)

Squid was a British World War II ship-mounted anti-submarine weapon. It consisted of a three-barrelled mortar which launched depth charges. It replaced the Hedgehog system, and was in turn replaced by the Limbo system.

Literally ordered directly from the drawing board in 1942, under the auspices of the Directorate of Miscellaneous Weapons Development, this weapon was rushed into service in May 1943 on board HMS Ambuscade. The first production unit was installed on HMS Hadleigh Castle; it went on to be installed on 70 frigates and corvettes during the Second World War. The first successful use was by HMS Loch Killin on 31 July 1944, when she sank U333; the system was credited with sinking 17 submarines in 50 attacks. By 1959, 195 Squid installations had been produced.

This weapon was a three-barrel 12-inch (305 mm) mortar with the mortars mounted in series but off-bore from each other in order to scatter the projectiles. The barrels were mounted in a frame that could be rotated through 90 degrees for loading. The projectiles weighed 390 pounds (177 kg) with a 207-pound (94 kg) minol charge. On some vessels, the Squid installations were at the stern – the bombs were fired over the length of the ship and dropping into the sea slightly ahead of it. Sink rate was 43.5 ft/s (13.3 m/s) and a clockwork time fuze was used to determine the detonation depth; all three projectiles had to be set to the same depth; this could be continuously updated right up to the moment of launch to take into account the movements of the target. The maximum depth was 900 feet (270 m).

The weapons were automatically fired from the sonar range recorder at the proper moment. The pattern formed a triangle about 40 yards (37 m) on a side at a distance of 275 yards (250 m) ahead of the ship. Most Squid installations utilised two sets of mortars. All six bombs were fired in salvo so they formed opposing triangular spreads. The salvos were set to explode 25 feet (10 m) above and below the target, the resulting pressure wave crushing the hull of the submarine. Postwar trials found Squid was nine times more effective than conventional depth charges.Despite its proven effectiveness, some officers, notably Captain Kenneth Adams, RCN, opposed fitting Squid to escorts because it meant sacrificing guns, which would make ships unsuitable for fleet actions.In April 1977, the Type 61 frigate Salisbury became the last ship to fire Squid in Royal Navy service. Examples of the mortars are on display at the Explosion! Museum of Naval Firepower in Gosport, Hampshire and another at Devonport Naval Base. In addition, the system is fitted to HMS Cavalier (D73), which is part of the historic ships collection in the Historic Dockyard in Chatham, Kent.

In Swedish service the system soldiered on until 1982 when the Östergötland-class destroyers were decommissioned.

Squid Girl

Squid Girl, known in Japan as Shinryaku! Ika Musume (侵略!イカ娘, lit. Invade! Squid Girl) with the subtitle The invader comes from the bottom of the sea!, is a Japanese manga series by Masahiro Anbe, which was serialized in Akita Shoten's Weekly Shōnen Champion between July 2007 and February 2016. An anime television series adaptation by Diomedéa aired on TV Tokyo between October and December 2010, with a second season airing between September and December 2011. Three original video animation (OVA) episodes were released between 2012 and 2014.

Squid as food

Squid is eaten in many cuisines; in English, the culinary name calamari is often used for squid dishes but is also used for some octopus dishes as well, notably fried squid/octopus (fried calamari). There are many ways to prepare and cook squid, with every country and region having its own recipes. Fried squid appears in Mediterranean cuisine. In Lebanon, Syria and Armenia, it is served with a tarator sauce. In New Zealand, Australia and South Africa, it is sold in fish and chip shops. In North America, fried squid is a staple in seafood restaurants. In Britain, it can be found in Mediterranean 'calamari' or Asian 'salt and pepper fried squid' forms in all kinds of establishments, often served as a bar snack, street food or starter.

Squid can be prepared for consumption in other ways. In Korea, it is sometimes served raw, and elsewhere it is used as sushi, sashimi and tempura items, grilled, stuffed, covered in batter, stewed in gravy and served in stir-fries, rice, and noodle dishes. Dried shredded squid is a common snack in some Asian countries, including East Asia.

The Squid and the Whale

The Squid and the Whale is a 2005 American independent arthouse comedy-drama film written and directed by Noah Baumbach and produced by Wes Anderson. It tells the semi-autobiographical story of two boys in Brooklyn dealing with their parents' divorce in 1986. The film is named after the giant squid and sperm whale diorama housed at the American Museum of Natural History, which is seen in the film. The film was shot on Super 16mm, mostly using a handheld camera. At the 2005 Sundance Film Festival, the film won awards for best dramatic direction and screenwriting, and was nominated for the Grand Jury Prize. Baumbach later received an Academy Award nomination for Best Original Screenplay. The film received six Independent Spirit Award nominations and three Golden Globe nominations. The New York Film Critics Circle, Los Angeles Film Critics Association and the National Board of Review voted its screenplay the year's best.

Vampire squid

The vampire squid (Vampyroteuthis infernalis, lit. "vampire squid from Hell") is a small cephalopod found throughout temperate and tropical oceans in extreme deep sea conditions. Unique retractile sensory filaments justify the vampire squid's placement in its own order, Vampyromorphida, as it shares similarities with both octopuses and squid. As a phylogenetic relict, it is the only known surviving member of its order. The first specimens were collected on the Valdivia Expedition and they were originally described as an octopus in 1903 by German teuthologist Carl Chun, but later assigned to a new order together with several extinct taxa.

Principal commercial fishery species groups
Edible mollusks
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