| Cuttlefish | |
|---|---|
| Sepia latimanus, East Timor | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Superorder: | Decapodiformes |
| Order: | Sepiida Zittel, 1895 |
| Suborders and Families | |
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Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda (which also includes squid, octopuses, and nautiluses). Despite their name, cuttlefish are not fish but molluscs.
Cuttlefish have an internal shell (the cuttlebone), large W-shaped pupils, eight arms and two tentacles furnished with denticulated suckers, with which they secure their prey. They generally range in size from 15 cm (5.9 in) to 25 cm (9.8 in), with the largest species, Sepia apama, reaching 50 cm (20 in) in mantle length and over 10.5 kg (23 lb) in weight.[1]
Cuttlefish eat small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals, seabirds and other cuttlefish. Their life expectancy is about one to two years. Recent studies indicate that cuttlefish are among the most intelligent invertebrates.[2] Cuttlefish also have one of the largest brain-to-body size ratios of all invertebrates.[2]
The 'cuttle' in 'cuttlefish' comes from the Old English word cudele, meaning 'cuttlefish', which may be cognate with the Old Norse koddi ('cushion', 'testicle') and the Middle Low German küdel ('pouch'). The Greco-Roman world valued the cephalopod as a source of the unique brown pigment that the creature releases from its siphon when it is alarmed. The word for it in both Greek and Latin, sepia, is now used to refer to a brown pigment in English.
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Cuttlefish possess an internal structure called the cuttlebone, which is porous and is made of aragonite. This provides the cuttlefish with buoyancy, which it regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the ventral siphuncle.[3] 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. Jewelers and silversmiths traditionally use cuttlebones as moulds for casting small objects,[4] but they are probably better known as the tough material given to parakeets and other caged birds as a source of dietary calcium.
Cuttlefish are sometimes referred to as the "chameleon of the sea" because of their remarkable ability to rapidly alter their skin color at will. Cuttlefish change color and light polarisation to communicate to other cuttlefish and to camouflage themselves 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, which corresponds to about 359 DPI. The pigmented chromatophores have a sac of pigment and a large membrane that is folded when retracted. There are 6 to 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 light as it 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.[5]
Cuttlefish eyes are among the most developed in the animal kingdom. The organogenesis of cephalopod eyes differs fundamentally from that of vertebrates like humans.[6] 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 cuttlefish cannot see color,[7] 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 foveae), one to look more forward, and one to look more backward. The eye changes focus by reshaping the entire eye, instead of reshaping the lens as in mammals. Unlike the vertebrate eye, there is no blind spot, because the optic nerve is positioned behind the retina.
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.[8]
The suckers of cuttlefish extend most of the length of their arms and along the distal portion of their tentacles.
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 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.
Cuttlefish have ink, like squid and octopuses, which they use to help evade predators.
Like octopuses and some squid, all cuttlefish have bacterially-produced neurotoxins in their saliva.[9]
The muscles of Pfeffer's Flamboyant Cuttlefish contain a highly toxic compound that is yet to be identified.[2] 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.[10]
While the preferred diet of cuttlefish is crabs and fish, they feed on small shrimp shortly after hatching.[11]
They use their camouflage to hunt and sneak up on their prey. When they get close enough, they open their eight arms and shoot out two long feeding tentacles. On the end of each is a pad covered in suckers that grabs and pulls prey toward its beak.[11]
Family Sepiidae, which contains all cuttlefish, inhabit tropical/temperate ocean waters. They are mostly shallow-water animals although they are known to go to depths of about 600 metres (2,000 ft).[12] 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. 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.[13]
Over 120 species of cuttlefish are currently recognised, grouped into 5 genera. Sepiadariidae contains seven species and 2 genera; all the rest are in Sepiidae.
Cuttlefish are caught for food in the Mediterranean, 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 popular snack food.
Cuttlefish are especially popular in Italy, where they are used in Risotto al Nero di Seppia (literally black cuttlefish rice). 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 rice turns because of the cuttlefish ink.
In Spain, breaded and deep-fried cuttlefish is a popular dish in Andalusia, where it is known as choco. 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 Portugal, it is the regional dish of the city of Setúbal and surrounding areas, where it is served as deep-fried strips or in a variant of feijoada, with red kidney beans.
Eugenio Montale's ground-breaking debut collection of poetry Cuttlefish Bones (Ossi di seppia) was 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 ink was formerly an important dye, called sepia. Today artificial dyes have mostly replaced natural sepia.
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