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Cuttlefish or cuttles are marine
molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...
of the order Sepiida. They belong to the
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
Cephalopoda which also includes squid, octopuses, and
nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in ...
es. Cuttlefish have a unique internal
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
, the
cuttlebone Cuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure (an internal shell) found in all members of the family Sepiidae, commonly known as cuttlefish, within the cephalopods. In other cephalopod families it is calle ...
, which is used for control of
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...
. Cuttlefish have large, W-shaped
pupil The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...
s, eight
arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...
s, and two
tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work ma ...
s furnished with denticulated suckers, with which they secure their prey. They generally range in size from , with the largest species, the
giant cuttlefish Giant cuttlefish also known as the Australian giant cuttlefish (scientific name ''Sepia apama''), is the world's largest cuttlefish species, growing to in mantle length and up to in total length (total length meaning the whole length of the ...
(''Sepia apama''), reaching in mantle length and over in mass. Cuttlefish eat small molluscs, crabs, shrimp, fish, octopus, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals, seabirds, and other cuttlefish. The typical life expectancy of a cuttlefish is about 1–2 years. Studies are said to indicate cuttlefish to be among the most intelligent
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s.NOVA, 2007. Cuttlefish: Kings of Camouflage.
(television program) NOVA, PBS, April 3, 2007. Cuttlefish also have one of the largest brain-to-body size ratios of all invertebrates. The "cuttle" in cuttlefish comes from the
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th c ...
name for the species, ''cudele'', which may be cognate with the
Old Norse Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and their overseas settlemen ...
''koddi'' (cushion) and the
Middle Low German Middle Low German or Middle Saxon (autonym: ''Sassisch'', i.e. " Saxon", Standard High German: ', Modern Dutch: ') is a developmental stage of Low German. It developed from the Old Saxon language in the Middle Ages and has been documented i ...
''Kudel'' (rag). The Greco-Roman world valued the cuttlefish as a source of the unique brown
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
the creature releases from its siphon when it is alarmed. The word for it in both
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
and
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, ''sepia'', now refers to the reddish-brown color
sepia Sepia may refer to: Biology * ''Sepia'' (genus), a genus of cuttlefish Color * Sepia (color), a reddish-brown color * Sepia tone, a photography technique Music * ''Sepia'', a 2001 album by Coco Mbassi * ''Sepia'' (album) by Yu Takahashi * " ...
in English.


Fossil record

The earliest fossils of cuttlefish are from the end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
period, represented by '' Ceratisepia'' from the Late
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...
Maastricht Formation of the Netherlands. Although the Jurassic ''
Trachyteuthis ''Trachyteuthis'' is a genus of fossil cephalopod, comprising five species: ''T. hastiformis'', ''T. latipinnis'', ''T. nusplingensis'', ''T. teudopsiformis'', ''T. covacevichi'' and ''T. chilensis''. Taxonomy The taxonomic placement of ''Tr ...
'' was historically considered possibly related to cuttlefish, later studies considered to be more closely related to octopus and vampire squid.


Range and habitat

The family Sepiidae, which contains all cuttlefish, inhabits tropical and temperate ocean waters. They are mostly shallow-water animals, although they are known to go to depths of about . They have an unusual biogeographic pattern; they are present along the coasts of East and South Asia, Western Europe, and the Mediterranean, as well as all coasts of Africa and Australia, but are totally absent from the Americas. By the time the family evolved, ostensibly in the Old World, the North Atlantic possibly had become too cold and deep for these warm-water species to cross. The
common cuttlefish #REDIRECT Common cuttlefish #REDIRECT Common cuttlefish {{redirect category shell, {{R from other capitalisation{{R from move ...
{{redirect category shell, {{R from other capitalisation{{R from move ...
(''Sepia officinalis''), is found in the Mediterranean, North and Baltic seas, although populations may occur as far south as South Africa. They are found in
sublittoral The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal area ...
depths, between the low tide line and the edge of the continental shelf, to about . The cuttlefish is listed under the Red List category of "least concern" by the IUCN Red List of Threatened Species. This means that while some over-exploitation of the marine animal has occurred in some regions due to large-scale commercial fishing, their wide geographic range prevents them from being too threatened. Ocean acidification, however, caused largely by higher levels of carbon dioxide emitted into the atmosphere, is cited as a potential threat.


Anatomy and physiology


Visual system

Cuttlefish, like other cephalopods, have sophisticated eyes. The
organogenesis Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal org ...
and the final structure of the
cephalopod eye Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions.Budelmann BU. "Cephalopod sense organs, nerves and the brain: Adaptations for high performance and life style." Marine and Freshwater Behav ...
fundamentally differ from those of
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s such as humans. Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
. The cuttlefish pupil is a smoothly curving W-shape. Although cuttlefish cannot see color, they can perceive the
polarization of light Polarization ( also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of t ...
, which enhances their perception of contrast. They have two spots of concentrated sensor cells on their
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
s (known as foveae), one to look more forward, and one to look more backward. The eye changes focus by shifting the position of the entire lens with respect to the retina, instead of reshaping the lens as in mammals. Unlike the vertebrate eye, no blind spot exists, because the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
is positioned behind the retina. They are capable of using
stereopsis Stereopsis () is the component of depth perception retrieved through binocular vision. Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image becaus ...
, enabling them to discern depth/distance because their brain calculates the input from both eyes. The cuttlefish's eyes are thought to be fully developed before birth, and they start observing their surroundings while still in the egg. In consequence, they may prefer to hunt the prey they saw before hatching.


Circulatory system

The blood of a cuttlefish is an unusual shade of green-blue, because it uses the copper-containing protein
haemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2) ...
to carry oxygen instead of the red, iron-containing protein
haemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
found in vertebrates' blood. The blood is pumped by three separate hearts: two branchial hearts pump blood to the cuttlefish's pair of gills (one heart for each), and the third pumps blood around the rest of the body. Cuttlefish blood must flow more rapidly than that of most other animals because haemocyanin carries substantially less oxygen than haemoglobin. Unlike most other mollusks, cephalopods like cuttlefish have a closed circulatory system.


Cuttlebone

Cuttlefish possess an internal structure called the
cuttlebone Cuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure (an internal shell) found in all members of the family Sepiidae, commonly known as cuttlefish, within the cephalopods. In other cephalopod families it is calle ...
, which is porous and is made of
aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...
. The pores provide it with
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...
, which the cuttlefish regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
siphuncle. Each
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
' cuttlebone has a distinct shape, size, and pattern of ridges or texture. The cuttlebone is unique to cuttlefish, and is one of the features that distinguish them from their squid relatives.


Ink

Like other marine mollusks, cuttlefish have ink stores that are used for chemical deterrence, phagomimicry, sensory distraction, and evasion when attacked. Its composition results in a dark colored ink, rich in ammonium salts and
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s that may have a role in phagomimicry defenses. The ink can be ejected to create a "
smoke screen A smoke screen is smoke released to mask the movement or location of military units such as infantry, tanks, aircraft, or ships. Smoke screens are commonly deployed either by a canister (such as a grenade) or generated by a vehicle (such as ...
" to hide the cuttlefish's escape, or it can be released as a
pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...
of similar size to the cuttlefish, acting as a decoy while the cuttlefish swims away. Human use of this substance is wide-ranged. A common use is in cooking with squid ink to darken and flavor rice and pasta. It adds a black tint and a sweet flavor to the food. In addition to food, cuttlefish ink can be used with plastics and staining of materials. The diverse composition of cuttlefish ink, and its deep complexity of colors, allows for dilution and modification of its color. Cuttlefish ink can be used to make noniridescent reds, blues, and greens, subsequently used for
biomimetic Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from grc, βίος (''bios''), life, and μίμησ ...
colors and materials.


Arms and mantle cavity

Cuttlefish have eight arms and two additional elongated tentacles that are used to grasp prey. The elongated tentacles and mantle cavity serve as defense mechanisms; when approached by a predator, the cuttlefish can suck water into its mantle cavity and spread its arms in order to appear larger than normal. Though the mantle cavity is used for jet propulsion, the main parts of the body that are used for basic mobility are the fins, which can maneuver the cuttlefish in all directions.


Suckers and venom

The suckers of cuttlefish extend most of the length of their arms and along the distal portion of their tentacles. Like other cephalopods, cuttlefish have "taste-by-touch" sensitivity in their suckers, allowing them to discriminate among objects and water currents that they contact. Some cuttlefish are venomous. The genes for venom production are thought to be descended from a common ancestor. The muscles of the flamboyant cuttlefish (''
Metasepia pfefferi ''Metasepia pfefferi'', also known as the flamboyant cuttlefish, is a species of cuttlefish occurring in tropical Indo-Pacific waters off northern Australia, southern New Guinea, as well as numerous islands of the Philippines, Indonesia and Malay ...
'') contain a highly toxic, unidentified compound as lethal as that of a fellow cephalopod, the
blue-ringed octopus Blue-ringed octopuses, comprising the genus ''Hapalochlaena'', are four highly venomous species of octopus that are found in tide pools and coral reefs in the Pacific and Indian oceans, from Japan to Australia. They can be identified by their ye ...
.


Sleep-like behavior

Sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
is a state of immobility characterized by being rapidly reversible, homeostatically controlled, and increasing an organism's arousal threshold. To date one cephalopod species, ''Octopus vulgaris'', has been shown to satisfy these criteria. Another species, ''Sepia officinalis'', satisfies two of the three criteria but has not yet been tested on the third (arousal threshold). Recent research shows that the sleep-like state in a common species of cuttlefish, ''Sepia officinalis'', shows predictable periods of rapid eye movement, arm twitching and rapid chromatophore changes.


Lifecycle

The lifespan of a cuttlefish is typically around one to two years, depending on the species. They hatch from eggs fully developed, around long, reaching around the first two months. Before death, cuttlefish go through senescence when the cephalopod essentially deteriorates, or rots in place. Their eyesight begins to fail, which affects their ability to see, move, and hunt efficiently. Once this process begins, cuttlefish tend to not live long due to predation by other organisms.


Reproduction

Cuttlefish start to actively mate at around five months of age. Male cuttlefish challenge one another for dominance and the best den during mating season. During this challenge, no direct contact is usually made. The animals threaten each other until one of them backs down and swims away. Eventually, the larger male cuttlefish mate with the females by grabbing them with their tentacles, turning the female so that the two animals are face-to-face, then using a specialized tentacle to insert sperm sacs into an opening near the female's mouth. As males can also use their funnels to flush others' sperm out of the female's pouch, the male then guards the female until she lays the eggs a few hours later. After laying her cluster of eggs, the female cuttlefish secretes ink on them making them look very similar to grapes. The egg case is produced through a complex capsule of the female accessory genital glands and the ink bag. On occasion, a large competitor arrives to threaten the male cuttlefish. In these instances, the male first attempts to intimidate the other male. If the competitor does not flee, the male eventually attacks it to force it away. The cuttlefish that can paralyze the other first, by forcing it near its mouth, wins the fight and the female. Since typically four or five (and sometimes as many as 10) males are available for every female, this behavior is inevitable.Mating Trick: Science Videos
Science News – ScienCentral Cuttlefish are indeterminate growers, so smaller cuttlefish always have a chance of finding a mate the next year when they are bigger. Additionally, cuttlefish unable to win in a direct confrontation with a guard male have been observed employing several other tactics to acquire a mate. The most successful of these methods is camouflage; smaller cuttlefish use their camouflage abilities to disguise themselves as a female cuttlefish. Changing their body color, and even pretending to be holding an egg sack, disguised males are able to swim past the larger guard male and mate with the female.


Communication

Cephalopods are able to communicate visually using a diverse range of signals. To produce these signals, cephalopods can vary four types of communication element: chromatic (skin coloration), skin texture (e.g. rough or smooth), posture, and locomotion. Changes in body appearance such as these are sometimes called
polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyphe ...
. The common cuttlefish can display 34 chromatic, six textural, eight postural and six locomotor elements, whereas flamboyant cuttlefish use between 42 and 75 chromatic, 14 postural, and seven textural and locomotor elements. The
Caribbean reef squid The Caribbean reef squid (''Sepioteuthis sepioidea''), commonly called the reef squid, is a species of small, torpedo-shaped squid with undulating fins that extend nearly the entire length of the body, approximately in length. In 2001, marine b ...
(''Sepioteuthis sepioidea'') is thought to have up to 35 distinct signalling states.


Chromatic

As with real chameleons, cuttlefish are sometimes referred to as the "
chameleons Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...
of the sea" because of their ability to rapidly alter their skin color – this can occur within one second. Cuttlefish change color and pattern (including the polarization of the reflected light waves), and the shape of the skin to communicate to other cuttlefish, to
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
themselves, and as a
deimatic display Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey anim ...
to warn off potential predators. Under some circumstances, cuttlefish can be trained to change color in response to stimuli, thereby indicating their color changing is not completely innate. Cuttlefish can also affect the light's polarization, which can be used to signal to other marine animals, many of which can also sense polarization, as well as being able to influence the color of light as it reflects off their skin. Although cuttlefish (and most other cephalopods) lack color vision, high-resolution polarisation vision may provide an alternative mode of receiving contrast information that is just as defined. The cuttlefish's wide pupil may accentuate chromatic aberration, allowing it to perceive color by focusing specific wavelengths onto the retina. The three broad categories of color patterns are uniform, mottle, and disruptive. Cuttlefish can display as many as 12 to 14 patterns, 13 of which have been categorized as seven "acute" (relatively brief) and six "chronic" (long-lasting) patterns. although other researchers suggest the patterns occur on a continuum. The color-changing ability of cuttlefish is due to multiple types of cells. These are arranged (from the skin's surface going deeper) as
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
ed
chromatophore Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, ...
s above a layer of reflective iridophores and below them,
leucophore Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contras ...
s.


Chromatophores

The
chromatophores Chromatophores are cells that produce color, of which many types are Biological pigment, pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and ...
are sacs containing hundreds of thousands of pigment granules and a large membrane that is folded when retracted. Hundreds of muscles radiate from the chromatophore. These are under neural control and when they expand, they reveal the hue of the pigment contained in the sac. Cuttlefish have three types of chromatophore: yellow/orange (the uppermost layer), red, and brown/black (the deepest layer). The cuttlefish can control the contraction and relaxation of the muscles around individual chromatophores, thereby opening or closing the elastic sacs and allowing different levels of pigment to be exposed. Furthermore, the chromatophores contain luminescent protein nanostructures in which tethered pigment granules modify light through absorbance, reflection, and
fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
between 650 and 720 nm. For cephalopods in general, the hues of the pigment granules are relatively constant within a species, but can vary slightly between species. For example, the common cuttlefish and the opalescent inshore squid (''
Doryteuthis opalescens ''Doryteuthis opalescens'', the opalescent inshore squid or market squid, is a small squid (mantle length (ML) up to 190 mm) in the family Loliginidae. It is a myopsid squid, which is the near shore group and that means that they have cor ...
'') have yellow, red, and brown, the European common squid (''
Alloteuthis subulata ''Alloteuthis subulata'', the European common squid, is a species of squid in the family Loliginidae. Distribution ''Alloteuthis subulata'' is found in the eastern Atlantic Ocean as far south as North-west Africa, the North Sea, the western Ba ...
'') has yellow and red, and the
common octopus The common octopus (''Octopus vulgaris'') is a mollusc belonging to the class Cephalopoda. ''Octopus vulgaris'' is one of the most studied of all octopus species, and also one of the most intelligent. It ranges from the eastern Atlantic, exte ...
has yellow, orange, red, brown, and black. In cuttlefish, activation of a chromatophore can expand its surface area by 500%. Up to 200 chromatophores per mm2 of skin may occur. In ''Loligo plei'', an expanded chromatophore may be up to 1.5 mm in diameter, but when retracted, it can measure as little as 0.1 mm.


Iridophores

Retracting the chromatophores reveals the iridophores and leucophores beneath them, thereby allowing cuttlefish to use another modality of visual signalling brought about by
structural coloration Structural coloration in animals, and a few plants, is the production of colour by microscopically structured surfaces fine enough to interfere with visible light instead of pigments, although some structural coloration occurs in combination wi ...
. Iridophores are structures that produce iridescent colors with a metallic sheen. They reflect light using plates of crystalline chemochromes made from
guanine Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
. When illuminated, they reflect iridescent colors because of the diffraction of light within the stacked plates. Orientation of the chemochromes determines the nature of the color observed. By using biochromes as colored filters, iridophores create an optical effect known as
Tyndall Tyndall (the original spelling, also Tyndale, "Tindol", Tyndal, Tindoll, Tindall, Tindal, Tindale, Tindle, Tindell, Tindill, and Tindel) is the name of an English family taken from the land they held as tenants in chief of the Kings of Engla ...
or
Rayleigh scattering Rayleigh scattering ( ), named after the 19th-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of th ...
, producing bright blue or blue-green colors. Iridophores vary in size, but are generally smaller than 1 mm. Squid at least are able to change their iridescence. This takes several seconds or minutes, and the mechanism is not understood. However, iridescence can also be altered by expanding and retracting the chromatophores above the iridophores. Because chromatophores are under direct neural control from the brain, this effect can be immediate. Cephalopod iridophores polarize light. Cephalopods have a rhabdomeric visual system which means they are visually sensitive to polarized light. Cuttlefish use their polarization vision when hunting for silvery fish (their scales polarize light). Female cuttlefish exhibit a greater number of polarized light displays than males and also alter their behavior when responding to polarized patterns. The use of polarized reflective patterns has led some to suggest that cephalopods may communicate intraspecifically in a mode that is "hidden" or "private" because many of their predators are insensitive to polarized light.


Leucophores

Leucophores, usually located deeper in the skin than iridophores, are also structural reflectors using crystalline
purines Purine is a heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines a ...
, often guanine, to reflect light. Unlike iridophores, however, leucophores have more organized crystals that reduce diffraction. Given a source of white light, they produce a white shine, in red they produce red, and in blue they produce blue. Leucophores assist in camouflage by providing light areas during background matching (e.g. by resembling light-colored objects in the environment) and disruptive coloration (by making the body appear to be composed of high-contrasting patches). The reflectance spectra of cuttlefish patterns and several natural substrates ( stipple,
mottle Mottle is a pattern of irregular marks, spots, streaks, blotches or patches of different shades or colours. It is commonly used to describe the surface of plants or the skin of animals. In plants, mottling usually consists of yellowish spots o ...
, disruptive) can be measured using an optic
spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
.


Intraspecific

Cuttlefish sometimes use their color patterns to signal future intent to other cuttlefish. For example, during agonistic encounters, male cuttlefish adopt a pattern called the intense zebra pattern, considered to be an
honest signal Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is when organisms with conflicting interests, such as in sex ...
. If a male is intending to attack, it adopts a "dark face" change, otherwise, it remains pale. In at least one species, female cuttlefish react to their own reflection in a mirror and to other females by displaying a body pattern called "splotch". However, they do not use this display in response to males, inanimate objects, or prey. This indicates they are able to discriminate same-sex
conspecifics Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
, even when human observers are unable to discern the sex of a cuttlefish in the absence of
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
. Female cuttlefish signal their receptivity to mating using a display called precopulatory grey. Male cuttlefish sometimes use deception toward guarding males to mate with females. Small males hide their
sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
fourth arms, change their skin pattern to the mottled appearance of females, and change the shape of their arms to mimic those of nonreceptive, egg-laying females. Displays on one side of a cuttlefish can be independent of the other side of the body; males can display courtship signals to females on one side while simultaneously showing female-like displays with the other side to stop rival males interfering with their courtship.


Interspecific

The deimatic display (a rapid change to black and white with dark ‘eyespots’ and contour, and spreading of the body and fins) is used to startle small fish that are unlikely to prey on the cuttlefish, but use the flamboyant display towards larger, more dangerous fish, and give no display at all to
chemosensory A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecep ...
predators such as crabs and dogfish. One dynamic pattern shown by cuttlefish is dark mottled waves apparently repeatedly moving down the body of the animals. This has been called the passing cloud pattern. In the common cuttlefish, this is primarily observed during hunting, and is thought to communicate to potential prey – “stop and watch me” – which some have interpreted as a type of "hypnosis".


Camouflage

Cuttlefish are able to rapidly change the color of their skin to match their surroundings and create chromatically complex patterns, despite their inability to perceive color, through some mechanism which is not completely understood. They have been seen to have the ability to assess their surroundings and match the color, contrast and texture of the substrate even in nearly total darkness. The color variations in the mimicked substrate and animal skin are similar. Depending on the species, the skin of cuttlefish responds to substrate changes in distinctive ways. By changing naturalistic backgrounds, the camouflage responses of different species can be measured. ''Sepia officinalis'' changes color to match the substrate by disruptive patterning (contrast to break up the outline), whereas '' S. pharaonis'' matches the substrate by blending in. Although camouflage is achieved in different ways, and in an absence of color vision, both species change their skin colors to match the substrate. Cuttlefish adapt their own camouflage pattern in ways that are specific for a particular habitat. An animal could settle in the sand and appear one way, with another animal a few feet away in a slightly different
microhabitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
, settled in algae for example, will be camouflaged quite differently. Cuttlefish are also able to change the texture of their skin. The skin contains bands of circular muscle which as they contract, push fluid up. These can be seen as little spikes, bumps, or flat blades. This can help with camouflage when the cuttlefish becomes texturally as well as chromatically similar to objects in its environment such as kelp or rocks.


Diet

While the preferred diet of cuttlefish is crabs and fish, they feed on small shrimp shortly after hatching. Cuttlefish use their camouflage to hunt and sneak up on their prey. They swim at the bottom, where shrimp and crabs are found, and shoot out a jet of water to uncover the prey buried in the sand. Then when the prey tries to escape, the cuttlefish open their eight arms and shoot out two long feeding tentacles to grab them. Each arm has a pad covered in suckers, which grabs and pulls prey toward its beak, paralyzing it with venom before eating it.Cuttlefish Basics
Tonmo.com (2003-02-12). Retrieved on 2011-09-18. Cuttlefish have also been observed to change color rapidly when they hunt, with an apparent hypnotic or confusing effect on some prey.


Taxonomy

Over 120
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of cuttlefish are currently recognised, grouped into six
families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
divided between two suborders. One suborder and three families are extinct. *Order Sepiida: cuttlefish **Suborder † Vasseuriina ***Family † Vasseuriidae ***Family † Belosepiellidae **Suborder Sepiina ***Family † Belosaepiidae ***Family Sepiadariidae ***Family
Sepiidae Sepiidae is a family of cephalopods in the order Sepiida. Classification *Order Sepiida: cuttlefish **Family Sepiadariidae **Family Sepiidae ***Genus ''Metasepia'' ****''Metasepia pfefferi'', flamboyant cuttlefish ****'' Metasepia tullbergi' ...
***Family Sepiolidae File:Sepia officinalis (aquarium).jpg, The
common cuttlefish #REDIRECT Common cuttlefish #REDIRECT Common cuttlefish {{redirect category shell, {{R from other capitalisation{{R from move ...
{{redirect category shell, {{R from other capitalisation{{R from move ...
(''Sepia officinalis'') is the best-known cuttlefish species File:Hooded Cuttlefish.jpg, Hooded cuttlefish (''Sepia prashadi'') File:Seba molluscas.jpg, Engravings by the Dutch zoologist
Albertus Seba Albertus or Albert Seba (May 12, 1665, Etzel near Friedeburg – May 2, 1736, Amsterdam) was a Dutch pharmacist, zoologist, and collector. Seba accumulated one of the largest cabinets of curiosities in the Netherlands during his time. He sold ...
, 1665–1736


Human uses


As food

Cuttlefish are caught for food in the Mediterranean, East Asia, the English Channel, and elsewhere. In East Asia, dried, shredded cuttlefish is a popular snack food. In the
Qing Dynasty The Qing dynasty ( ), officially the Great Qing,, was a Manchu-led imperial dynasty of China and the last orthodox dynasty in Chinese history. It emerged from the Later Jin dynasty founded by the Jianzhou Jurchens, a Tungusic-spea ...
manual of Chinese
gastronomy Gastronomy is the study of the relationship between food and culture, the art of preparing and serving rich or delicate and appetizing food, the cooking styles of particular regions, and the science of good eating. One who is well versed in gastr ...
, the ''
Suiyuan shidan Recipes from the Garden of Contentment () is a work on cooking and gastronomy written by the Qing dynasty, Qing-dynasty painter and poet Yuan Mei. It is known in English under various titles, including ''Food Lists of the Garden of Contentment'', ...
'', the roe of the cuttlefish, is considered a difficult-to-prepare, but sought-after delicacy. Cuttlefish are quite popular in Europe. For example, in northeast Italy, they are used in ''
risotto Risotto (, , from meaning "rice") is a northern Italian rice dish cooked with broth until it reaches a creamy consistency. The broth can be derived from meat, fish, or vegetables. Many types of risotto contain butter, onion, white wine, and Pa ...
al nero di seppia'' (risotto with cuttlefish ink), also found in Croatia and Montenegro as ''crni rižot'' (black risotto). Catalan cuisine, especially that of the coastal regions, uses cuttlefish and squid ink in a variety of ''
tapas A tapa () is an appetizer or snack in Spanish cuisine. Tapas can be combined to make a full meal, and can be cold (such as mixed olives and cheese) or hot (such as ''chopitos'', which are battered, fried baby squid, or patatas bravas). In so ...
'' and dishes such as '' arròs negre''. Breaded and deep-fried cuttlefish is a popular dish in
Andalusia Andalusia (, ; es, Andalucía ) is the southernmost autonomous community in Peninsular Spain. It is the most populous and the second-largest autonomous community in the country. It is officially recognised as a "historical nationality". The t ...
. In
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
, cuttlefish is present in many popular dishes. ''Chocos com tinta'' (cuttlefish in black ink), for example, is grilled cuttlefish in a sauce of its own ink. Cuttlefish is also popular in the region of
Setúbal Setúbal (, , ; cel-x-proto, Caetobrix) is a city and a municipality in Portugal. The population in 2014 was 118,166, occupying an area of . The city itself had 89,303 inhabitants in 2001. It lies within the Lisbon metropolitan area. In the ti ...
, where it is served as deep-fried strips or in a variant of ''
feijoada ''Feijoada'' () is a stew of beans with beef and pork. The name ''feijoada'' comes from ''feijão'', 'bean' in Portuguese. It is widely prepared in the Portuguese-speaking world, with slight variations. The basic ingredients of feijoada are bean ...
'', with white beans. Black pasta is often made using cuttlefish ink.


Sepia

Cuttlefish ink was formerly an important dye, called
sepia Sepia may refer to: Biology * ''Sepia'' (genus), a genus of cuttlefish Color * Sepia (color), a reddish-brown color * Sepia tone, a photography technique Music * ''Sepia'', a 2001 album by Coco Mbassi * ''Sepia'' (album) by Yu Takahashi * " ...
. To extract the sepia pigment from a cuttlefish (or squid), the ink sac is removed and dried then dissolved in a dilute alkali. The resulting solution is filtered to isolate the pigment, which is then precipitated with dilute hydrochloric acid. The isolated precipitate is the sepia pigment. It is relatively chemically inert, which contributes to its longevity. Today, artificial dyes have mostly replaced natural sepia.


Metal casting

Cuttlebone has been used since antiquity to make casts for metal. A model is pushed into the cuttlebone and removed, leaving an impression. Molten gold, silver or pewter can then be poured into the cast.


Smart clothing

Research into replicating biological color-changing has led to engineering artificial chromatophores out of small devices known as dielectric elastomer actuators. Engineers at the
University of Bristol , mottoeng = earningpromotes one's innate power (from Horace, ''Ode 4.4'') , established = 1595 – Merchant Venturers School1876 – University College, Bristol1909 – received royal charter , type ...
have engineered soft materials that mimic the color-changing skin of animals like cuttlefish, paving the way for "smart clothing" and camouflage applications.


Pets

Though cuttlefish are rarely kept as pets, due in part to their fairly short lifetimes, the most common to be kept are '' Sepia officinalis'' and '' Sepia bandensis''.Ceph Care , TONMO.com: The Octopus News Magazine Online
. TONMO.com. Retrieved on 2015-09-25. Cuttlefish may fight or even eat each other if there is inadequate tank space for multiple individuals. Cuttlebone is given to
parakeet A parakeet is any one of many small to medium-sized species of parrot, in multiple genera, that generally has long tail feathers. Etymology and naming The name ''parakeet'' is derived from the French wor''perroquet'' which is reflected in ...
s and other
cagebird Aviculture is the practice of keeping and breeding birds, especially of wild birds in captivity. Types There are various reasons that people get involved in aviculture. Some people breed birds to preserve a species. Some people breed parrots a ...
s as a source of dietary
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
.


See also

*
Cephalopod size Cephalopods vary enormously in size. The smallest are only about long and weigh less than at maturity, while the largest—the giant and colossal squids—can exceed in length and weigh close to half a tonne (), making them the largest living ...


References


External links


YouTube video with examples of cuttlefish color and texture modulations
*
The new CEPHBASE within the Encyclopedia of Life (EOL)
{{Taxonbar, from=Q184479 Commercial molluscs Articles containing video clips Cenozoic cephalopods