WHAT IS A CUTTLEFISH?

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Cuttlefish are molluscs.  They belong to the marine order Sepiida and class Cephalopoda, along with octopuses, squid and nautiluses. But rather than living in the open water like squid they stick close to the ground. 

They get their name from the strange cuttle bone, an internal shell that runs along the length of their body.  This bone is porous and made of aragonite. It provides buoyancy to the cuttlefish, which is regulated by a change of gas to liquid ratio in the chamber. Cuttlefish bone is often collected on the beach and sold in pet shops as a dietary aid to caged parrots and birds as it is high in calcium. 

Cuttlefish have eight arms and two tentacles, which are covered with tiny tentacle suckers. They often weigh several kilograms but the largest species, Sepia apama, can weigh over 10 kg (23 llb).  They range in size from 15 to 25 cm but can reach 50 cm in length.

Cuttlefish move mainly by a fin line that runs around their entire body.  They feed on small molluscs, shrimp, crabs, octopuses and other small sea creatures.  Like octopuses cuttlefish are capable of sudden colour changes, which they use as camouflage and also to signal their moods. They control their colour through groups of red, black, brown and yellow pigment cells called chromatophores.  Each square millimetre of the skin is covered with up to 200 of these specialised colour changing cells.

Cuttlefish can live up to two years.  They are intelligent creatures, having the largest brain to body ratio of all the invertebrates. Each species is distinctive in its shape, size and pattern of ridges. They have sophisticated eyes and distinctive ‘w’ shaped pupils, which means that they cannot see colour but can see forward and backwards. Like their cousins the octopus and squid, cuttlefish also have ink which they use to help evade predators.

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