Cuttlefish or cuttles are #marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes #squid , #octopuses , and nautiluses. Cuttlefish have a #unique internal #shell , the cuttlebone, which is used for control of #buoyancy .

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

Cuttlefish #eat small molluscs , #crabs , #shrimp , #fish , #octopus , #worms , and other cuttlefish. Their #predators include #dolphins , #sharks , #fish , #seals , #seabird s, 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 intelligent invertebrates. Cuttlefish also have one of the largest brain-to-body size ratios of all #invertebrates .

The "cuttle" in cuttlefish comes from the Old #English name for the species, cudele, which may be cognate with the Old Norse koddi (cushion) and the Middle Low #German Kudel (rag). The Greco-Roman #world valued the cuttlefish as a source of the unique brown pigment the #creature releases from its siphon when it is alarmed. The word for it in both #Greek and #Latin , #sepia , now refers to the reddish-brown color sepia in English.

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 , #NorthSea and #BalticSea , although #populations may occur as far south as #SouthAfrica . They are found in sublittoral 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 #carbondioxide emitted into the #atmosphere , is cited as a potential threat.

Cuttlefish, like other cephalopods, have sophisticated eyes. The organogenesis and the final #structure of the cephalopod #eye fundamentally differ from those of #vertebrates such as #humans . Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of convergent #evolution . The cuttlefish pupil is a #smoothly curving W-shape. Although cuttlefish cannot see #color , they can perceive the polarization of #light , which enhances their perception of contrast. They have two spots of concentrated #sensor #cells on their retinas (known as foveae), 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 #blindspot exists, because the #optic nerve is positioned behind the retina. They are capable of using stereopsis, 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 .

The #lifespan of a cuttlefish is typically around one to two years, depending on the species. They hatch from eggs fully developed, around 6 mm (1⁄4 in) long, reaching 25 mm (1 in) around the first two months. Before #death , cuttlefish go through #senescence when the cephalopod essentially deteriorates, or rots in place. Their #eyesight begins to fail, which affects their ability to see, move, and hunt efficiently. Once this process begins, cuttlefish tend to not live long due to predation by other #organisms .

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Source: #Wikipedia

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