Cephalopods - Cuttlefish

Cuttlefish belong to the Cephalopods. They are usually found in shallow watersand around reefs along the coasts of east and south Asia, western Europe, the Mediterranean, Africa and Australia. They are among the most intelligent invertebrates.

Cuttlefish have an internal shell (the cuttlebone), large W-shaped pupils, and eight arms and two tentacles.They normally range in size from 15 cm to 25 cm. tThe largest species, The Australian Giant Cuttlefish (Sepia apama) grows to 60 cm in mantle length and over 10.5 kg in weight.

The Australian Giant Cuttlefish is native to the southern coast of Australia, from Brisbane in Queensland to Shark Bay in Western Australia. It occurs on rocky reefs, seagrass beds, and sand and mud seafloor to a depth of 100 m.

Cuttlefish have two methods of swimming. They can jet propel themselves backwards by sucking water into their body cavity and then expelling it through a funnel. This produces a very rapid backward movement, which is usually used for escaping predators as it is needs a great deal of energy. .Hovering and normal swimming is achieved by gentle wave-like movements of their side fins.

Cuttlefish eyes are among the most developed in the animal kingdom although they cannot see colour. They have two spots of concentrated sensor cells on their retina, one to look to the front, 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.

Cuttlefish change colour to communicate with other cuttlefish and to camouflage themselves. The colour changing is produced by groups of red, yellow, brown, and black pigmented chromatophores which are placed above special light-refelcting cells. The chromatophores can produce a wide range of colours, for example orange is produced by red and yellow chromatophores,

The cuttlebone is porous and is made of aragonite, a form of calcium carbonate. This provides the cuttlefish with buoyancy which can be controlled by changing the amount of air in the chambers inside the cuttlebone. Each species has a distinct shape, size, and pattern of ridges or texture on the cuttlebone. Cuttlebones are often found washed up on beaches and are fed to caged birds as a source of calcium in their diets.

Cuttlefish live for somewhere between 18 and 24 months and the females die shortly after spawning. Mating cuttlefish place their bodies head to head so the male can transfer a sealed package of sperm into a pouch beneath the female's mouth. The female then finds a quiet place where she draws eggs from her cavity and passes them over the sperm to fertilise them.

Cuttlefish attach clusters of around 200 eggs, coated with squid ink (sepia) which acts as a glue and also camouflages them. After 2 to 4 months the young hatch as tiny versions of their parents with a supply of yolk that nourishes them until their first catch of prey.

The main prey for cuttlefish are small fish, molluscs, crustaceans (such as prawns and small crabs), octopuses, worms, and other cuttlefish. They usually feed at night. To feed, the cuttlefish shoot out, in a rapid whip-like action, two long feeding tentacles normally retracted in pouches under their eyes. On the end of eachtentacle is a pad covered in suckers.

They eat their prey holding it with their arms. If they are feeding on an animal with a hard shell, they use their strong beaks to crack open the shell and their radula (tooth-lined tongue) for rasping away at the food.

When attacked by predators(e.g. dolphins, seals, fish, sharks and other cuttlefish) cuttlefish can produce a cloud of black ink to confuses the predator, allowing the cuttlefish to escape. They can also camouflage themselves to hide from their predators, and to ambush their prey. This camouflage can be seen in the changing of colours and patterns, caused by a layer of chromatophores (tiny elastic pigment sacs) found just under the skin.