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'Cuttlefish' are marine animals of the order 'Sepiida' belonging to the Cephalopoda class (which also includes squid, octopuses, and nautiluses). Despite their common name, cuttlefish are not fish but molluscs. Recent studies indicate that cuttlefish may be the most intelligent invertebrate species. NOVA, 2007. Cuttlefish: Kings of Camouflage. (television program) NOVA, PBS, April 3, 2007.
Cuttlefish have an internal shell (cuttlebone), large W shaped eyes, and eight arms and two tentacles furnished with denticulated suckers, with which they secure their prey.
Cuttlefish eat small molluscs, crabs, shrimp, fish and other cuttlefish. Their predators include dolphins, sharks, fish, seals and other cuttlefish. They live about 1 to 2 years.

Contents

Anatomy

Cuttlebone

Changing color

Eyes

Blood

Toxicity

Ink

As food

In literature

Classification

References

External links

Anatomy

Cuttlebone

Main articles: Cuttlebone

Cuttlefish possess an internal structure called the cuttlebone, which is porous and composed of calcium carbonate, to provide the cuttlefish with buoyancy. Buoyancy can be regulated by changing the gas-to-liquid ratio in the chambered cuttlebone. Each species has a distinct shape, size, and pattern of ridges or texture on the "bone". 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 cage birds as a source of dietary calcium. The cuttlebone is unique to cuttlefish, one of the features contrasting them with their squid relatives.

Changing color

Cuttlefish are sometimes called 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 cells 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

Cuttlefish eyes are among the most developed in the animal kingdom. The organogenesis of cephalopod eyes differs fundamentally from that of vertebrates like humans.^[1]
Superficial similarities between cephalopod and vertebrate eyes are examples of convergent evolution. The cuttlefish pupil is a smoothly-curving W shape. Although they cannot see color,^[2] 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 instead pulled around by reshaping the entire eye in order to change focus.

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 the Museum Victoria in Queensland, Australia has shown the toxin to be as lethal as that of a fellow cephalopod, the Blue-ringed octopus.^[3]

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.

As food

Cuttlefish are caught for food in the Mediterranean and East Asia. 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 Italy, where it is used in ''Risotto Nero''. The Croatian ''Crni Rižot'' is virtually the same recipe, which probably originated in Venice and then spread across both coasts of the Adriatic. "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 literature

Cuttlefish made their most important literary appearance in the title of Eugenio Montale's ground-breaking debut collection of poetry entitled ''Cuttlefish Bones'' (''Ossi di seppia''), published in Turin in 1925. Montale, who grew up in Liguria along the Mediterranean Sea, 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 poetry.
In the popular novel ''Twenty Thousand Leagues Under the Sea'' by Jules Verne, Captain Nemo and his companions engage in a fierce battle with a group of giant cuttlefish. Although the creatures are defeated, one of the crew members is killed during the fight. Although Jules Verne accurately describes the cuttlefish's three hearts, he describes their blood as being red, instead of its actual greenish tint.

Classification

''Sepia officinalis'' from Turkish waters

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.

★ CLASS CEPHALOPODA

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★ Subclass Nautiloidea: nautilus

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★ Subclass Coleoidea: squid, octopus, cuttlefish

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★ Superorder Octopodiformes

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★ Superorder Decapodiformes

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★ ?Order †Boletzkyida

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★ Order Spirulida: Ram's Horn Squid

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★ Order 'Sepiida': cuttlefish

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★ Suborder †Vasseuriina

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★ Family †Vasseuriidae

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★ Family †Belosepiellidae

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★ Suborder Sepiina

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★ Family †Belosaepiidae

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★ Family Sepiadariidae

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★ Family Sepiidae

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★ Order Sepiolida: bobtail squid

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★ Order Teuthida: squid

References

1. "Development of the Eye in Vertebrates and Cephalopods and Its Implications for Retinal Structure"
2. "Color blindness and contrast perception in cuttlefish (Sepia offcinalis) determined by a visual sensorimotor assay"
3. Teacher's Guide to NOVA episode - Kings of Camouflage on PBS (After Watching: Activity 2).

External links

★ Scientific Database with photos and videos of cuttlefish and other cephalopods

★ TONMO.com offers articles and forum discussion on cuttlefish care

★ YouTube video of a cuttlefish harassing a diver

★ YouTube video of cuttlefish hovering about. You can see colour changes and movement.

★ YouTube video with excellent examples of color and texture modulation.

★ Amazing cuttlefish - Cephalopods with natural camouflage and sepia ink

★ Diving with cuttlefish

★ PBS.org - Nova - Kings of Camouflage

★ Google Video - Nova - Kings of Camouflage