Cuttlefish, or cuttles, are of the Sepiina. They belong to the which also includes , , and . Cuttlefish have a unique internal , the , which is used for control of .

Cuttlefish
Temporal range: Maastrichtian– recent

Cuttlefish have large, W-shaped , eight , and two furnished with suckers, with which they secure their prey. They generally range in size from 15 to 25 cm (6 to 10 in), with , the (Sepia apama), reaching 50 cm (20 in) in length and over 10.5 kg (23 lb) in mass.

Cuttlefish eat small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Their predators include dolphins, larger fish (including sharks), seals, seabirds, and other cuttlefish. The typical life expectancy of a cuttlefish is about 1–2 years. Studies are said to indicate cuttlefish to be among the most .Cuttlefish also have one of the largest ratios of all invertebrates.

The valued the cuttlefish as a source of the unique brown the creature releases from its when it is alarmed. The word for the cuttlefish in both and , sepia, now refers to the reddish-brown color in English.

Fossil record

The earliest fossils of cuttlefish are from the end of the period, represented by from the Late of the Netherlands. Although the Jurassic was historically considered possibly related to cuttlefish, later studies considered it to be more closely related to octopuses and vampire squids.

Range and habitat

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 (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 depths, between the low tide line and the edge of the continental shelf, to about 180 m (600 ft). The cuttlefish is listed under the Red List category of "least concern" by the IUCN Red List of Threatened Species. This means that while some over-exploitation of the marine animal has occurred in some regions due to large-scale commercial fishing, their wide geographic range prevents them from being too threatened. Ocean acidification, however, caused largely by higher levels of carbon dioxide emitted into the atmosphere, is cited as a potential threat. Some studies suggest that ocean acidification does not impair normal embryonic development, survival rates or body size.

Anatomy and physiologyCuttleboneMain article: Top and bottom view of a cuttlebone, the buoyancy organ and internal shell of a cuttlefish

Unlike other cephalopods, cuttlefish possess a unique internal structure called the , a highly modified internal shell, which is porous and is made of . Except for , they are the only coleoid cephalopods with a shell with a divided into chambers separated by septa. The pores provide it with , which the cuttlefish regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the . Each ' 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.

Visual systemCuttlefish, like other cephalopods, have sophisticated eyes. The and the final structure of the fundamentally differ from those of , such as humans. Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of . The cuttlefish pupil is a smoothly curving W-shape. Although cuttlefish cannot see color, they can perceive the , which enhances their perception of . They have two spots of concentrated sensor cells on their (known as ), one to look more forward, and one to look more backward. The eye changes focus by shifting the position of the entire lens with respect to the retina, instead of reshaping the lens as in mammals. Unlike the vertebrate eye, no exists, because the is positioned behind the retina. They are capable of using , enabling them to discern depth/distance because their brain calculates the input from both eyes.

The cuttlefish's eyes are thought to be fully developed before birth, and they start observing their surroundings while still in the egg. In consequence, they may prefer to hunt the prey they saw before hatching.

Arms and mantle cavity

Cuttlefish have eight arms and two additional elongated tentacles that are used to grasp prey. The elongated tentacles and mantle cavity serve as defense mechanisms; when approached by a predator, the cuttlefish can suck water into its mantle cavity and spread its arms in order to appear larger than normal. Though the mantle cavity is used for jet propulsion, the main parts of the body that are used for basic mobility are the fins, which can maneuver the cuttlefish in all directions.

Suckers

The of cuttlefish extend most of the length of their arms and along the distal portion of their tentacles. Like other cephalopods, cuttlefish have "taste-by-touch" sensitivity in their suckers, allowing them to discriminate among objects and water currents that they contact.

Circulatory system

The blood of a cuttlefish is an unusual shade of green-blue, because it uses the copper-containing protein to carry oxygen instead of the red, iron-containing protein found in vertebrates' blood. The blood is pumped by three separate hearts: two pump blood to the cuttlefish's pair of gills (one heart for each), and the third pumps blood around the rest of the body. Cuttlefish blood must flow more rapidly than that of most other animals because haemocyanin carries substantially less oxygen than haemoglobin. Unlike most other mollusks, cephalopods like cuttlefish have a circulatory system.

Ink

Like other marine mollusks, cuttlefish have ink stores that are used for chemical deterrence, , sensory distraction, and evasion when attacked. Its composition results in a dark colored ink, rich in salts and that may have a role in phagomimicry defenses.The ink can be ejected to create a "" to hide the cuttlefish's escape, or it can be released as a of similar size to the cuttlefish, acting as a decoy while the cuttlefish swims away.

Human use of this substance is wide-ranged. A common use is in cooking with squid ink to darken and flavor rice and pasta. It adds a black tint and a sweet flavor to the food. In addition to food, cuttlefish ink can be used with plastics and staining of materials.[] The diverse composition of cuttlefish ink, and its deep complexity of colors, allows for dilution and modification of its color. Cuttlefish ink can be used to make noniridescent reds, blues, and greens, subsequently used for colors and materials.[]

Poison and venom

A common gene between cuttlefish and almost all other cephalopods allows them to produce venom, excreting it through their beak to help kill their prey. Additionally, the muscles of the flamboyant cuttlefish () contain a highly toxic, unidentified compound as lethal as the venom of fellow cephalopod, the .However, this toxin is found only in the muscle and is not injected in any form, classifying it as poisonous, not venomous.

Sleep-like behavior

is a state of immobility characterized by being rapidly reversible, homeostatically controlled, and increasing an organism's arousal threshold.

To date 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.