THE OCEAN DEEP

Cuttlefish are much more closely related to garden slugs and snails than they are to fish! They belong to the same group of animals as the octopuses, squid and nautilus and like a snail they are all molluscs. Cuttlefish are unique within this group in that they have a gas filled bone within their bodies which allows them to be buoyant... you may have seen cuttlebones before, sticking out from the bars on a budgie's cage? The bone is within the body part of the animal called the mantle and attached to the mantle is a head with eight arms and two feeding tentacles. he cuttlefish is an ambush predator and a master of disguise. Its skin is covered with special cells called chromatophores, iridophores and leucophores that reflect light in many different colours enabling the cuttlefish to blend into its background almost perfectly. Some say it's like a chameleon but it is far superior in its ability to change colour and even the texture of its skin! A cuttlefish will steadily, using its camouflage, sneak up on its prey. Their preferred diet is crabs or fish, and when it is close enough it opens apart its eight arms and out shoots two deceptively long feeding tentacle. On the end of each is a pad covered in suckers that grasp hold of the prey and quickly pull it close to the cuttlefish's mouth that looks like a parrot's beak. The scientific name for a cuttlefish is Sepia. In years gone by sepia ink, which is derived from cuttlefish, was used by artists for their paintings. For the cuttlefish this ink is a decoy, a means of escape from predators. If a large fish were to attack a cuttlefish it would eject a cloud of dark brown, almost black ink towards its attacker! The predator would get a mouthful of ink that tastes nasty and coats its nostrils. Meanwhile the cuttlefish is hidden from view and propels itself away backwards by using its own jet propulsion system, its siphon.
The eggs of cuttlefish are laid in clumps together and are often coated in ink from the mother; this serves as camouflage for the eggs. They hatch at a much further developed stage than an octopus does and immediately start feeding on suitably small shrimps. Many people would like to keep cuttlefish as pets. This is quite easy in the UK and Europe as species of cuttlefish like Sepia officinalis the 'European cuttlefish' are found there.
In the USA however, there are no naturally found species and the most commonly imported species is from Bali called Sepia bandensis which is a poor traveller and normally arrives as a four-inch adult with perhaps only weeks to live. It is not recommended as a pet. One day someone will be captive breeding Sepia officinalis for the American hobby!
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 and snails as a source of dietary calcium
Changing color
Cuttlefish are photochromic, and 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 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. 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 in order 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.
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.