Cuttlefish, or simply cuttles, are marine cephalopods distinguished by a unique internal shell called the cuttlebone, a porous aragonite structure that serves as a buoyancy control organ. Moreover, they also have highly developed eyes with W-shaped pupils capable of detecting polarized light. They constitute the family Sepiidae.
Often called the ‘chameleons of the sea,’ cuttlefish can rapidly change the color, pattern, and texture of their skin for camouflage, communication, and defense. This remarkable ability arises from the presence of specialized pigment and reflective cells embedded within their skin.
They possess three separate hearts, and their blood has an unusual green-blue hue due to the presence of the copper-based pigment haemocyanin.
They typically measure around 6 to 10 in (15 to 25 cm) in mantle length. One of the smallest species, the dwarf cuttlefish (Ascarosepion bandense), is barely 1.5 to 2.7 in (4 to 7 cm) long (in terms of mantle length) as adults, whereas the largest, the giant cuttlefish (Ascarosepion apama), grows up to 20 in (50 cm).[1][2]
These cephalopods typically have an oval-shaped, somewhat dorsoventrally flattened body. They possess a porous, aragonite structure, the cuttlebone, which functions as a buoyancy control organ. This structure lies along the dorsal side of the muscular mantle, just beneath the skin.
They possess ten appendages in total. There are eight short, muscular arms surrounding the mouth and two long, highly specialized, retractable tentacles used to capture prey. In males, the fourth arm on the left side, known as the hectocotylus, is modified for the transfer of sperm to the females.
Each of the arms is lined with suckers along most of its length. The specialized tentacles have suckers only at their tips, forming a flattened, club-like end.
Like other cephalopods, they have well-developed eyes. Their pupils are W-shaped, and they have two spots of densely packed sensor cells (fovea) on their retina. They can only detect polarized light, lacking the capacity for color vision.
Below the head and between the bases of the arms lies a funnel-like opening, the siphon, through which waste and water are eliminated. Close to the siphon lies a muscular ink sac, which produces a dark-colored ink, rich in ammonium salts and amino acids.
The skin of cuttlefish is embedded with three layers of specialized cells, each contributing to the overall body color. The outermost layer comprises the chromatophores, which are tiny elastic sacs filled with pigment granules (imparting colors like orange, yellow, red, black, and brown). Each sac radiates hundreds of radial muscles that are under direct neural control. When these muscles contract, the sac expands, revealing the pigment color.
Beneath the chromatophores lies the layer of iridophores comprising crystalline plates made of guanine. These plates reflect iridescent colors such as blue, green, or metallic hues through structural coloration.
The deepest layer, lying under the iridiophores, comprises leucophores, which, like iridiophores, are structural reflectors typically composed of guanine. They reflect ambient light, producing colors that help them blend into their surroundings.
As of 2025, the World Register of Marine Species notes 116 species of cuttlefish classified into 13 genera.
For decades, most cuttlefish species were grouped under Sepia, with only a few exceptions, such as Sepiella and Metasepia. However, a 2023 study revealed that Sepia was not monophyletic, meaning not all species shared a single common ancestor within that group. Thus, the authors split Sepia into several monophyletic genera, like Acanthosepion, Ascarosepion, Rhombosepion, and others. The list given above, hence, shows the new genera while keeping the species binomials with Sepia.
The remaining species (not listed above) require a taxonomic review.
The earliest fossils of cuttlefish date back to the Late Cretaceous Period. They are represented by members of the genus Ceratisepia, unearthed from the Maastricht Formation of the Netherlands.
Cuttlefish are primarily found in temperate and tropical marine waters of the world. Their range is quite distinctive, with no wild populations in the Americas. However, they are abundant in the Mediterranean Sea, eastern Atlantic Ocean, the Indian Ocean, and parts of the Western Pacific, including Australia, Japan, and Southeast Asia.
Although cuttlefish generally inhabit shallow waters, the depth at which they live varies among species. For example, the golden cuttlefish (Sepia esculenta) is typically found between 33 and 492 ft (10 and 150 m), whereas the knifebone cuttlefish (Sepia cultrata) can occur at depths of about 2,620 ft (800 m).[3][4]
They are carnivorous predators that typically feed on crabs, shrimp, snails, octopuses, and marine worms.
Most of these cephalopods typically survive 1 to 2 years in the wild, though the giant cuttlefish lives up to 4 years.[7][8]
Male cuttlefish try to attract their female counterparts by flashing vibrant colors across their bodies using their chromatophores. They challenge other males by threatening each other with their tentacles until one surrenders. The dominant male eventually grabs the female with his arms, turns her, such that they remain face-to-face while copulating. He then transfers sacs of sperm (spermatophore) to an opening near the female’s mouth using his specialized tentacle. The male continues to guard the female till she is ready to lay her eggs in a few hours.
Depending on the species, the female lays up to 1,000 eggs in clusters, eventually secreting ink on them (giving them the appearance of a bunch of black grapes). In 30 to 90 days, the eggs hatch into juveniles (about 0.25 inches long) and begin feeding on small shrimp soon after. These juveniles grow indeterminately, gradually developing gonads and the cuttlebone. They attain sexual maturity in about 7 to 18 months, depending on the species.
They are preyed upon by predatory dolphins, such as Commerson’s dolphin (Cephalorhynchus commersonii), several sharks, seals, and seabirds, including penguins.[9]
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