Cuttlefish

Unlike other cephalopods, cuttlefish possess a unique internal structure called the cuttlebone, a highly modified internal shell, which is porous and is made of aragonite. Except for Spirula, they are the only coleoid cephalopods with a shell with a phragmocone divided into chambers separated by septa. The pores provide it with buoyancy, which the cuttlefish regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the ventral siphuncle. Each species' cuttlebone has a distinct shape, size, and pattern of ridges or texture. The cuttlebone is unique to cuttlefish, and is one of the features that distinguish them from their squid relatives.

The family Sepiidae, which contains all cuttlefish, inhabits tropical and temperate ocean waters. They are mostly shallow-water animals, although they are known to go to depths of about 600 m (2,000 ft). They have an unusual biogeographic pattern; they are present along the coasts of East and South Asia, Western Europe, and the Mediterranean, as well as all coasts of Africa and Australia, but are totally absent from the Americas. By the time the family evolved, ostensibly in the Old World, the North Atlantic possibly had become too cold and deep for these warm-water species to cross. The common cuttlefish (Sepia officinalis), is found in the Mediterranean, North and Baltic seas, although populations may occur as far south as South Africa. They are found in sublittoral depths, between the low tide line and the edge of the continental shelf, to about 180 m (600 ft).

Sleep is a state of immobility characterized by being rapidly reversible, homeostatically controlled, and increasing an organism's arousal threshold. One cephalopod species, Octopus vulgaris, has been shown to satisfy these criteria. Another species, Sepia officinalis, satisfies two of the three criteria but has not yet been tested on the third (arousal threshold). Recent research shows that the sleep-like state in a common species of cuttlefish, Sepia officinalis, shows predictable periods of rapid eye movement, arm twitching and rapid chromatophore changes.

Cuttlefish are caught for food in the Mediterranean, Asia, the English Channel, and elsewhere.

In East Asia, dried, shredded cuttlefish is a popular snack food. In the Qing Dynasty manual of Chinese gastronomy, the Suiyuan shidan, the roe of the cuttlefish, is considered a difficult-to-prepare, but sought-after delicacy. Cuttlefish thick soup is a signature dish in Taiwan.

In Southeast Asia, cuttlefish is a regional dish typical of the Sundanese people in west Java, Indonesia, known as balakutak. The dish is squid stir-fried with various spices and mixed with its ink.

In Sri Lanka, hot butter cuttlefish (batter fried cuttlefish stir fried with butter, chilli flakes, capsicums, and spring onions) is a popular dish that can be found anywhere in the country, usually served as a starter together with drinks.