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. [1]
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.
Anatomy
Cuttlebone
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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
An infant cuttlefish protects itself with camouflage
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
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.[2] 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,[3] 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. [1] 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.[4]
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.[citation needed]
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
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.
References
External links
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