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Cuttlefish are marine animals of the order Sepiida belonging to the class Cephalopoda (which also includes squid, octopuses, and nautiluses). Despite their common name, cuttlefish are not fish but mollusks. Recent studies indicate that cuttlefish are among the most intelligent invertebrates.

The origin of the word cuttlefish can be found in the old English term cudele, itself derived in the 1400s from the Norwegian koddi (tentacle) and the Middle German kudel (pouch), a literal description of the cephalopod's shape. The Greco-Roman world valued the cephalopod as a source of the unique brown pigment released from its siphon when alarmed. Hence, the word for it in Greek and Latin is sepia (later seppia in Italian).

Cuttlefish have an internal shell (the cuttlebone), large W-shaped pupils, and eight arm and two tentacles furnished with denticulated suckers, with which they secure their prey.

Cuttlefish generally range in size from to , with the largest species, Sepia apama, reaching in mantle length and over in weight.

Cuttlefish eat small mollusc, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals and other cuttlefish. Their life expectancy is about one to two years.

Anatomy

Cuttlebone

Cuttlefish possess an internal structure called the cuttlebone, which is porous and composed of aragonite, to provide the cuttlefish with buoyancy. Buoyancy can be regulated by changing the gas-to-liquid ratio in the chambered cuttlebone via the ventral siphuncle. Each species has a distinct shape, size, and pattern of ridges or texture on the cuttlebone. The cuttlebone is unique to cuttlefish, one of the features contrasting them with their squid relatives. Cuttlebones are traditionally used by jewelers and silversmiths as moulds for casting small objects. They are probably better known today as the tough material given to parakeets and other caged birds as a source of dietary calcium.



Changing color

An infant cuttlefish protects itself with camouflage
Cuttlefish are sometimes referred to as the chameleon of the sea because of their remarkable ability to rapidly alter their skin color at will. Their skin flashes a fast-changing pattern as communication to other cuttlefish and to camouflage them from predators. This color-changing function is produced by groups of red, yellow, brown, and black pigmented chromatophores above a layer of reflective iridophores and leucophores, with up to 200 of these specialized pigment cell per square millimeter. The pigmented chromatophores have a sac of pigment and a large membrane that is folded when retracted. There are 6-20 small muscle cells on the sides which can contract to squash the elastic sac into a disc against the skin. Yellow chromatophores (xanthophores) are closest to the surface of the skin, red and orange are below (erythrophores), and brown or black are just above the iridophore layer (melanophores). The iridophores reflect blue and green light. Iridophores are plates of chitin or protein, which can reflect the environment around a cuttlefish. They are responsible for the metallic blues, greens, golds, and silvers often seen on cuttlefish. All of these cells can be used in combinations. For example, orange is produced by red and yellow chromatophores, while purple can be created by a red chromatophore and an iridophore. The cuttlefish can also use an iridophore and a yellow chromatophore to produce a brighter green. As well as being able to influence the color of the light that reflects off their skin, 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.

Eyes

A close up of a cuttlefish eye.
Cuttlefish eyes are among the most developed in the animal kingdom. The organogenesis of cephalopod eyes differs fundamentally from that of vertebrates like humans.Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of convergent evolution. The cuttlefish pupil is a smoothly-curving W shape. Although they cannot see color, they can perceive the polarization of light, which enhances their perception of contrast. They have two spots of concentrated sensor cells on their retina (known as fovea), one to look more forward, and one to look more backwards. The lenses, instead of being reshaped as they are in humans, are pulled around by reshaping the entire eye to change focus.

Scientists have speculated that cuttlefish's eyes are fully developed before birth and start observing their surroundings while still in the egg. One team of French researchers has additionally suggested that cuttlefish prefer to hunt the prey they saw before hatching.

Blood

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 that is found in mammals. The blood is pumped by three separate hearts, two of which are used for pumping blood to the cuttlefish's pair of gills (one heart for each gill), and the third for pumping blood around the rest of the body. A cuttlefish's heart must pump a higher blood flow than most other animals because hemocyanin is substantially less capable of carrying oxygen than hemoglobin.

Toxicity

Recently it has been discovered that the Pfeffer's Flamboyant Cuttlefish's muscles contain a highly toxic compound that is yet to be identified. Research by Mark Norman with Museum Victoria in Victoria, Australia, has shown the toxin to be as lethal as that of a fellow cephalopod, the Blue-ringed octopus.

Ink

Cuttlefish have ink, like squid and octopuses. This ink was formerly an important dye, called sepia. Today artificial dyes have replaced natural sepia. However, there is a modern resurgence of Jewish people using the ink for the techelet dye on their Tallit strings.

Distribution

Family Sepiidae, which contains all cuttlefish, has a tropical/temperate distribution. They are mostly shallow-water animals although they are known from depths of about 600 m . They have an unusual biogeographic pattern: totally absent from the Americas, but present along the coasts of east and south Asia, western Europe, the Mediterranean, as well as all coasts of Africa and Australia. Young et al. (1998) suggest that by the time the family evolved ostensibly in the Old World, the northern Atlantic had become too cold and deep for these warm water species to cross.

Classification

There are over 120 species of cuttlefish currently recognised, grouped into 5 genera. Sepiadariidae contains seven species and 2 genera; all the rest are in Sepiidae.



As food



Cuttlefish are caught for food in the Mediterraneanmarker, East Asia, the English Channel and elsewhere. Although squid is more popular as a restaurant dish all over the world, in East Asia dried shredded cuttlefish is a highly popular snack food.

Cuttlefish is especially popular in Italymarker, where it is used in Risotto al Nero di Seppia (literally black cuttlefish rice). The Croatianmarker Crni Rižot is virtually the same recipe, which probably originated in Venice and then spread across both coasts of the Adriaticmarker. "Nero" and "Crni" mean black, the color the rice turns because of the cuttlefish ink. Spanish cuisine, especially that of the coastal regions, uses cuttlefish and squid ink for the marine flavor and smoothness it provides; it is included in dishes such as rice, pasta and fish stews.

In Portugalmarker, it is the regional dish of the city of Setúbalmarker and surrounding areas, where it is served as deep-fried strips or in a variant of feijoada, with red kidney beans.

Cultural significance

Eugenio Montale's ground-breaking debut collection of poetry Cuttlefish Bones (Ossi di seppia) was published in Turinmarker in 1925. Montale, who grew up in Liguria along the Mediterranean Seamarker, was awarded the Nobel Prize for Literature in 1975, for his long and prolific career. Cuttlefish Bones remains one of the best-known and influential collections of 20th-century Italian poetry.

References

  1. NOVA, 2007. Cuttlefish: Kings of Camouflage. (television program) NOVA, PBS, April 3, 2007.
  2. Reid, A., P. Jereb, & C.F.E. Roper 2005. Family Sepiidae. In: P. Jereb & C.F.E. Roper, eds. Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 57–152.
  3. Casting Silver with Cuttlefish
  4. Teacher's Guide to NOVA episode - Kings of Camouflage on PBS (After Watching: Activity 2).
  5. Lu, C. C. and C. F. E. Roper, 1991. Aspects of the biology of Sepia cultrata from southeastern Australia. In: La Seiche, The Cuttlefish. Boucaud-Camou, E. (Ed). Caen, France; Centre de Publications de l'Université de Caen: 192.
  6. Young, R. E., M. Vecchione and D. Donovan, 1998. The evolution of coleoid cephalopods and their present biodiversity and ecology. South African Jour. Mar. Sci., 20: 393-420.


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