cuttlefish

Any of a family, Sepiidae, of squidlike cephalopods with an internal calcareous shell (cuttlebone). The common cuttle Sepia officinalis of the Atlantic and Mediterranean is up to 30 cm/1 ft long. It swims actively by means of the fins into which the sides of its oval, flattened body are expanded, and jerks itself backwards by shooting a jet of water from its ‘siphon’.

It is capable of rapid changes of colour and pattern. The large head has conspicuous eyes, and the ten arms are provided with suckers. Two arms are very much elongated, and with them the cuttlefish seizes its prey. It has an ink sac from which a dark fluid can be discharged into the water, distracting predators from the cuttle itself. The dark brown pigment sepia is obtained from the ink sacs of cuttlefish.

US biologists announced in 1999 the discovery of ultraviolet-absorbing compounds in the eyes of cuttlefish Sepia officinalis. This was the first time such compounds, which provide a natural sunblock, have been identified in the eyes of invertebrates (they had previously been known in some fish).