The Common cuttlefish Sepia officinalis has a broad, slightly flattened pouch-like body that can be up to 30cm long. Its beaked mouth is surrounded by eight arms plus two feeding tentacles. Although it is known as a cuttlefish, it is not a fish at all.

The Cuttlefish is a truly extraordinary marine species and is considered to be highly intelligent¹ due to the size of its brain in comparison to the size of its body.

Description

The cuttlefish is closely related to the squids, octopuses and the nautilus. All of these marine animals are in the group cephalopods, which means 'head foot'. In turn cephalopods are all molluscs which includes animals such as the oyster, the clam, the garden snail and the limpet.

For the biologists among you, or the plain curious the animal is in:

• Phylum Mollusca
• Class Cephalopoda
• Order Sepiida
• Genus Sepia
• Species Sepia officinalis

This list of latin terms is known as biological classification.

The main feature that differentiates the cuttlefish from the squid is that it has a gas-filled bone which allows the animal to be buoyant in water. This white 'cuttlebone'² is the internalised shell common to all molluscs (apart from the octopus). It is made from mineral calcium carbonate, in the form of aragonite. The finely chambered spaces of the cuttlebone allow the amount of gas-to-water to be regulated by the animal in order to achieve the correct level of buoyancy. These bones are frequently found washed up on beaches, as remnants of the animal.

The eyes of the cuttlefish are well-developed and extremely large for the size of the animal. These are some of the most highly-evolved eyes of all the animal species on the planet and are capable of seeing in the murky conditions of the seabed.

Cuttlefish also possess an ink sac, containing a very dark brown liquid which is used as a defence mechanism. When a predator such as a large fish attacks, the cuttlefish will eject a cloud of sepia ink; this acts as a decoy and distraction allowing the cuttlefish time to escape. Sepia ink has been used in artwork and as a writing ink. It gave its name to the delicate tones of old 'sepia photographs'. Various forms of black pasta are made by adding sepia ink to the dough mixture.

Habitat

Cuttlefish can be found in the shallow waters along the English Channel, throughout the Mediterranean Sea, down the Atlantic Ocean, following the West African coastline to its southernmost tip.

They are mostly to be found lying on the bottom of the sea, in camouflage, waiting for something to come along that they can catch and eat. They catch their prey by lying in ambush, using their prehensile feeding tentacles to shoot out and grab hold of small animals such as crabs or small fish.

Movement

The cuttlefish normally swims by using an undulating fin on the lower side of its body, which looks like a frilly skirt. If it needs to escape quickly it has a jet-propulsion system. When startled it can escape by assuming a shape for maximum streamlining and thrusting quickly forwards through the water whilst simultaneously releasing a cloud of murky sepia ink behind it to distract its predator. To shoot forward like this the cuttlefish draws water into a special cavity within its body and then forcibly squeezes it out using powerful muscles through an exit called a 'funnel'.

Camouflage

Cuttlefish have impressive control over their colour³, superior to chameleons, and can change the pattern and shade of their skin almost instantly to match their surroundings. Cuttlefish can easily adapt to textured surroundings such as a gravel sea bed and blend perfectly within seconds. To further aid their camouflage the cuttlefish can slightly bury themselves into the gravel and sand of a sea bed so that only a small part of it is exposed.

Life-Cycle

During mating the male Cuttlefish displays zebra-like stripes in order to warn off competing males and to impress the female. One of the arms on the male cuttlefish is specially adapted to pass a packet of sperm to the female.

After mating the female will lay her eggs, which are about 1 - 2cm in diameter, one by one over a period of time. She will incorporate a small amount of sepia ink into each egg to help disguise them. Once all the eggs are laid the female plays no further part in their development nor in the care of the newly-hatched young. In fact her duty is done, the life-cycle is completed and she will soon die. The approximate life expectancy of a cuttlefish is less than two years.

Culinary Uses

Like its close relations, the octopus and squid, cuttlefish are often caught and cooked - mainly in the Mediterranean. Many recipes which use squid as the main ingredient can be adapted to use with cuttlefish.