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Cephalopod ink is a dark pigment released into water by most species of cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the Nautilidae and the Cirrina (deep-sea octopuses),〔Roger T. Hanlon, John B. Messenger: ''Cephalopod Behaviour,'' page 2. Cambridge University Press, 1999, ISBN 0-521-64583-2〕 are able to release ink. The ink is released from the ink sacs (located between the gills) and is dispersed more widely by accompanying its release with a jet of water from the siphon. Its dark colour is caused by its main constituent, melanin. Each species of cephalopod produces slightly differently coloured inks; generally, octopuses produce black ink, squid ink is blue-black and cuttlefish ink is brown. A number of other aquatic molluscs have similar responses to attack, including the gastropod clade known as sea hares. ==Inking behaviours== Two distinct behaviours have been observed in inking cephalopods. The first is the release of large amounts of ink into the water by the cephalopod, in order to create a dark, diffuse cloud (much like a smoke screen) which can obscure the predator's view, allowing the cephalopod to make a rapid retreat by jetting away. The second response to a predator is to release pseudomorphs ("false bodies"); smaller clouds of ink with a greater mucus content, which allows them to hold their shape for longer. These are expelled slightly away from the cephalopod in question, which will often release several pseudomorphs and change colour (blanch) in conjunction with these releases. The pseudomorphs are roughly the same volume and look similar to the cephalopod that released them, and many predators have been observed attacking them mistakenly, allowing the cephalopod to escape (this behaviour is often referred to as the "blanch-ink-jet manoeuvre"). Furthermore, green turtle hatchlings (''Chelonia mydas'') that have been observed mistakenly attacking pseudomorphs released by ''Octopus bocki'' have subsequently ignored conspecific octopuses.〔Roy L. Caldwell (2005), "An Observation of Inking Behavior Protecting Adult ''Octopus bocki'' from Predation by Green Turtle (''Chelonia mydas'') Hatchlings" http://muse.jhu.edu/journals/pacific_science/v059/59.1caldwell.pdf〕 However, many cephalopod predators (for instance moray eels) have advanced chemosensory systems, and some anecdotal evidence〔G.E. MacGinitie, N. MacGinitie (1968) ''Natural History of Marine Animals'', Pages 395-397, 2nd ed. McGraw-Hill, New York.〕 suggests that compounds such as tyrosinase found in cephalopod ink can irritate, numb or even deactivate such apparatus. Unfortunately, few controlled experiments have been conducted to substantiate this. Cephalopod ink is nonetheless generally thought to be more sophisticated than a simple "smokescreen"; the ink of a number of squid and cuttlefish has been shown to function as a conspecific chemical alarm.〔Charles D. Derby (2007), "Escape by Inking and Secreting: Marine Molluscs Avoid Predators Through a Rich Array of Chemicals and Mechanisms" http://www.biolbull.org/cgi/reprint/213/3/274.pdf〕 Octopuses have also been observed squirting ink at snails or crabs approaching their eggs.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cephalopod ink」の詳細全文を読む スポンサード リンク
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