Cuttlefish

Taxonomy

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One hundred sixteen species of cuttlefish are currently recognized;^[7] for decades, the classification of this family relied on just three genera: Metasepia, Sepia, and Sepiella, with Sepia containing most of the species and several subgenera.^{[citation needed]} A 2023 paper shifted this perception by having recovered Sepia as containing several monophyletic groups or clades. The authors subsequently revived several synonymized genera and elevated some subgenera of Sepia to full genus level, reassigning many species of Sepia to these revived genera. Conversely, Metasepia was found to nest within one of these revived genera, and as it was named after Ascarosepion it became a junior synonym of that genus.^[8]

The genera and species of Sepiidae is as follows:^[7]

• Order Sepiida
  • Suborder Sepiina
    • Superfamily †Vasseurioidea
    • Superfamily Sepioidea
      • Family †Anomalosaepiidae Yancey & Garvie, 2011
      • Family †Belosaepiidae Dixon, 1850
      • Family Sepiidae
        • Genus Acanthosepion
          • Acanthosepion aculeata, needle cuttlefish (type)
          • Acanthosepion ellipticum, ovalbone cuttlefish
          • Acanthosepion esculentum, golden cuttlefish
          • Acanthosepion lycidas, kisslip cuttlefish
          • Acanthosepion pharaonis, Pharaoh cuttlefish
          • Acanthosepion ramani
          • Acanthosepion recurvirostrum, curvespine cuttlefish
          • Acanthosepion smithi, Smith's cuttlefish
          • Acanthosepion stelliferum
        • Genus Ascarosepion
          • Ascarosepion apama, giant Australian cuttlefish
          • Ascarosepion bandense, stumpy-spined cuttlefish
          • Ascarosepion cultratum, knifebone cuttlefish
          • Ascarosepion filibrachia
          • Ascarosepion latimanus, broadclub cuttlefish
          • Ascarosepion mestus, reaper cuttlefish (type)
          • Ascarosepion novaehollandiae, New Holland cuttlefish
          • Ascarosepion opipara
          • Ascarosepion papuensis, Papuan cuttlefish
          • Ascarosepion pfefferi, flamboyant cuttlefish
          • Ascarosepion plangon, mourning cuttlefish
          • Ascarosepion rozella, rosecone cuttlefish
          • Ascarosepion tullbergi, paintpot cuttlefish
        • Genus Aurosepina
          • Aurosepina arabica, Arabian cuttlefish
        • Genus Decorisepia
          • Sepia australis, southern cuttlefish
          • Sepia hedleyi, Hedley's cuttlefish (type)
          • Decorisepia madokai, Madokai's cuttlefish
        • Genus Digitosepia
          • Digitosepia barosei
          • Sepia dubia
          • Sepia faurei
          • Sepia robsoni (type)
          • Digitosepia shazaei
          • Digitosepia roeleveldi
        • Genus Doratosepion
          • Doratosepion andreana, Andrea cuttlefish (type)
          • Sepia braggi, slender cuttlefish
          • Sepia erostrata
          • Sepia foliopeza
          • Doratosepion kobiensis, Kobi cuttlefish
          • Sepia limata
          • Sepia longipes, longarm cuttlefish
          • Sepia lorigera, spider cuttlefish
          • Sepia pardex
          • Sepia peterseni
          • Sepia tenuipes
          • Sepia tokioensis
        • Genus Erythalassa
          • Erythalassa trygonina, trident cuttlefish
        • Genus Hemisepius
          • Hemisepius typicus
        • Genus Lusepia
          • Lusepia hieronis
        • Genus Rhombosepion
          • Sepia elegans, elegant cuttlefish (type)
          • Rhombosepion omani, Oman cuttlefish
          • Sepia orbignyana, pink cuttlefish
          • Sepia prashadi, hooded cuttlefish
        • Genus Sepia
          • Sepia hierredda
          • Sepia officinalis, common cuttlefish (type)
          • Sepia vermiculata
        • Genus Sepiella
          • Sepiella inermis, spineless cuttlefish
          • Sepiella japonica, Japanese spineless cuttlefish
          • Sepiella ornata, ornate cuttlefish (type, pending confirmation)
        • Genus Spathidosepion
          • Sepia angulata
          • Sepia papillata
          • Sepia tuberculata (type, pending genetic analysis)

The subsequent species are in need of taxonomic review, as they were not examined in the 2023 study.

• Sepiella cyanea
• Sepiella mangkangunga
• Sepiella ocellata

The species listed above with an asterisk (*) are questionable and need further study to determine if they are a valid species or a synonym. The question mark (?) indicates questionable placement within the genus.

Fossil record

The earliest fossils of cuttlefish are from the end of the Cretaceous period,^[10][11] represented by Ceratisepia from the Late Maastrichtian Maastricht Formation of the Netherlands.^[12] Although the Jurassic Trachyteuthis was historically considered possibly related to cuttlefish,^[13] later studies considered it to be more closely related to octopuses and vampire squids.^[14]

Cuttlebone

Top and bottom view of a cuttlebone, the buoyancy organ and internal shell of a cuttlefish

Unlike other cephalopods, cuttlefish possess a unique internal structure called the cuttlebone, a highly modified internal shell, which is porous and is made of aragonite. Except for Spirula, they are the only coleoid cephalopods with a shell with a phragmocone divided into chambers separated by septa.^[15] The pores provide it with buoyancy, which the cuttlefish regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the ventral siphuncle.^[16] Each species' 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.^[17]

Visual system

Cuttlefish, like other cephalopods, have sophisticated eyes. The organogenesis and the final structure of the cephalopod eye fundamentally differ from those of vertebrates, such as humans.^[18] Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of convergent evolution. The cuttlefish pupil is a smoothly curving W-shape.^[19][20] Although cuttlefish cannot see color,^[21] they can perceive the polarization of light, which enhances their perception of contrast. They have two spots of concentrated sensor cells on their retinas (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 is positioned behind the retina. They are capable of using stereopsis, enabling them to discern depth/distance because their brain calculates the input from both eyes.^[22][23]

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.^[24]

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.^[25] 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.^[26]

Suckers

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.^[27]

Circulatory system

The blood of a cuttlefish is an unusual shade of green-blue, because it uses the copper-containing protein hemocyanin to carry oxygen instead of the red, iron-containing protein hemoglobin 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 hemocyanin carries substantially less oxygen than hemoglobin. Unlike most other mollusks, cephalopods like cuttlefish have a closed circulatory system.^[28]

Ink

Like other marine mollusks, cuttlefish have ink stores that are used for chemical deterrence, phagomimicry, sensory distraction, and evasion when attacked.^[29] Its composition results in a dark colored ink, rich in ammonium salts and amino acids that may have a role in phagomimicry defenses.^[29] The ink can be ejected to create a "smoke screen" to hide the cuttlefish's escape, or it can be released as a pseudomorph of similar size to the cuttlefish, acting as a decoy while the cuttlefish swims away.^[30]

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.^{[citation needed]} 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,^[31] subsequently used for biomimetic colors and materials.^{[citation needed]}

Poison and venom

A common gene between cuttlefish and almost all other cephalopods allows them to produce venom, excreting it through their beak to help kill their prey.^[32] Additionally, the muscles of the flamboyant cuttlefish (Metasepa pfefferi) contain tetrodotoxin which is found to be the same as the blue-ringed octopus.^{[4][better source needed]} It is as lethal as the venom of fellow cephalopod, the blue-ringed octopus.^[33] However, this toxin is found only in the muscle and is not injected in any form, classifying it as poisonous, not venomous.^{[better source needed]}

Chromatic cells

Cuttlefish are sometimes referred to as the "chameleons 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 themselves, and as a deimatic display 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.^[34]

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.^[35] 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.^[36] The cuttlefish's wide pupil may accentuate chromatic aberration, allowing it to perceive color by focusing specific wavelengths onto the retina.^[37][38]

The three broad categories of color patterns are uniform, mottle, and disruptive.^[39] Cuttlefish can display as many as 12 to 14 patterns,^[40] 13 of which have been categorized as seven "acute" (relatively brief) and six "chronic" (long-lasting) patterns.^[41] although other researchers suggest the patterns occur on a continuum.^[39]

The color-changing ability of cuttlefish is due to multiple types of cells. These are arranged (from the skin's surface going deeper) as pigmented chromatophores above a layer of reflective iridophores and below them, leucophores.^[42][43]

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.

Iridophores are structures that produce iridescent colors with a metallic sheen. They reflect light using plates of crystalline chemochromes made from guanine. 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 or Rayleigh scattering, 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.^[49] 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.^[49][50][48]

Behavior

While the preferred diet of cuttlefish is crabs and fish, they feed on small shrimp shortly after hatching.^{[51][better source needed]}

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. 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.^[40][44]

Camouflage

Cuttlefish are able to rapidly change the color of their skin to match their surroundings and create chromatically complex patterns,^[60] despite their inability to perceive color, through some mechanism which is not completely understood.^[63] 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.^[47]

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.^[64] 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, settled in algae for example, will be camouflaged quite differently.^[47]

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.^[47]

Lifecycle

The lifespan of a cuttlefish is typically around one to two years, depending on the species. They hatch fully developed around 6 mm (1⁄4 in) long from eggs, reaching around 25 mm (1 in) after 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 directly impacts their ability to move and hunt efficiently. Once this process begins, cuttlefish tend not to live long due to predation by other organisms.

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—‍‌rather, 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.^[65] 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.^[66]

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.^[67]

Cuttlefish are indeterminate growers, so smaller cuttlefish always have a chance of finding a mate the next year when they are bigger.^[68] 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.^[67][69][57]

As food

Cuttlefish are caught for food in the Mediterranean, Asia, the English Channel, and elsewhere.

In East Asia, dried, shredded cuttlefish is a popular snack food. In the Qing Dynasty manual of Chinese gastronomy, the Suiyuan shidan, the roe of the cuttlefish, is considered a difficult-to-prepare, but sought-after delicacy.^[74] Cuttlefish thick soup is a signature dish in Taiwan.

In Southeast Asia, cuttlefish is a regional dish typical of the Sundanese people in west Java, Indonesia, known as balakutak. The dish is squid stir-fried with various spices and mixed with its ink.

In Sri Lanka, hot butter cuttlefish (batter fried cuttlefish stir fried with butter, chilli flakes, capsicums, and spring onions) is a popular dish that can be found anywhere in the country, usually served as a starter together with drinks.

Cuttlefish are quite popular in Europe. For example, in northeast Italy, they are used in risotto al nero di seppia (risotto with cuttlefish ink), also found in Croatia and Montenegro as crni rižot (black risotto), and in various recipes (either grilled or stewed) often served together with polenta. Catalan cuisine, especially that of the coastal regions, uses cuttlefish and squid ink in a variety of tapas and dishes such as arròs negre. Breaded and deep-fried cuttlefish is a popular dish in Andalusia. In Portugal, 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, where it is served as deep-fried strips or in a variant of feijoada, with white beans. Black pasta is often made using cuttlefish ink.

• 
  Cuttlefish with lemon (Spain)
• 
  Fried baby cuttlefish (Spain)
• 
  Risotto with cuttlefish ink (Italy)
• 
  Linguine with cuttlefish and ink sauce (Italy)
• 
  Cuttlefish roe soup (China)
• 
  Cuttlefish ink sausages (China)

Dye

Cuttlefish ink was formerly an important dye, called sepia.^[75] 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.^{[citation needed]} 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.^[76][77][78]

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 have engineered soft materials that mimic the color-changing skin of animals like cuttlefish,^[79] paving the way for "smart clothing" and camouflage applications.^[80]

Pets

Though cuttlefish are rarely kept as pets, due in part to their fairly short life expectancy, the most commonly kept are Sepia officinalis and Sepia bandensis.^[81] Cuttlefish may fight or even eat each other if there is inadequate tank space for multiple individuals.^[25]