![Chtenopteryx sicula2](https://upload.wikimedia.org/wikipedia/commons/8/85/Chtenopteryx_sicula2.jpg)
Cephalopod ink is a dark-coloured or luminous
ink
Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thicker ...
released into water by most species of
cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the
Nautilidae
The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.
It comprises six living species ...
and the
Cirrina
Cirrina or Cirrata is a suborder and one of the two main divisions of octopuses. Cirrate octopuses have a small, internal shell and two fins on their head, while their sister suborder Incirrina has neither. The fins of cirrate octopods are asso ...
(deep-sea octopuses), are able to release ink to confuse
predators
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
.
The ink is released from the
ink sac
An ink sac is an anatomical feature that is found in many cephalopod mollusks used to produce the defensive cephalopod ink. With the exception of nocturnal and very deep water cephalopods, all Coleoidea (squid, octopus and cuttlefish) which dwell ...
s (located between the
gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s) and is dispersed more widely when its release is accompanied by a jet of water from the
siphon. Its dark color is caused by its main constituent,
melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
. Each species of cephalopod produces slightly differently coloured inks; generally, octopuses produce black ink, squid ink is blue-black, and cuttlefish ink is a shade of brown.
A number of other aquatic molluscs have similar responses to attack, including the
gastropod clade known as
sea hare
The clade Anaspidea, commonly known as sea hares ('' Aplysia'' species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the ...
s.
Types of ink shapes
The shapes taken by ink releases are classified as six types:
* pseudomorphs;
* pseudomorph series;
* ink ropes;
* clouds/smokescreens;
* diffuse puffs;
* mantle fills.
Inking behaviors
Escape strategies
Two distinct behaviors 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
A smoke screen is smoke released to mask the movement or location of military units such as infantry, tanks, aircraft, or ships.
Smoke screens are commonly deployed either by a canister (such as a grenade) or generated by a vehicle (such as ...
) that 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
Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...
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 as 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"). Thus, such capture avoidance method is analogous to fighter jet dogfights where the followed pilot releases countermeasures (such as flares) to misdirect the sensors in some guided missiles.
Furthermore,
green turtle
The green sea turtle (''Chelonia mydas''), also known as the green turtle, black (sea) turtle or Pacific green turtle, is a species of large sea turtle of the family Cheloniidae. It is the only species in the genus ''Chelonia''. Its range exten ...
(''Chelonia mydas'') hatchlings that have been observed mistakenly attacking pseudomorphs released by ''
Octopus bocki
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
'' have subsequently ignored
conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
octopuses.
Hiding strategy
The
spotty bobtail squid releases ropes of ink longer than itself and hides among them, maybe to be confused with floating
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
leaves.
Behavior around eggs
Octopuses have also been observed squirting ink at
snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...
s or
crabs approaching their
eggs
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
.
Numerous cuttlefish species add a coat of ink to their eggs, presumably to camouflage them from potential predators.
Properties
Attack protection
Inking has been shown to protect species of squids against predatory fish attacks, as well during the capture phase as during the consummatory phase, due to visual and chemical effects of the ink releases.
Chemical effects
Many cephalopod predators (for instance
moray eel
Moray eels, or Muraenidae (), are a family of eels whose members are found worldwide. There are approximately 200 species in 15 genera which are almost exclusively marine, but several species are regularly seen in brackish water, and a few are f ...
s) have advanced
chemosensory systems, and some anecdotal evidence
[MacGinitie, G.E. and MacGinitie, N. (1968) ''Natural History of Marine Animals'', pp. 395–397, 2nd ed. McGraw-Hill, New York.] suggests that compounds (such as
tyrosinase
Tyrosinase is an oxidase that is the rate-limiting enzyme for controlling the production of melanin. The enzyme is mainly involved in two distinct reactions of melanin synthesis otherwise known as the Raper Mason pathway. Firstly, the hydroxy ...
) found in cephalopod ink can irritate, numb or even deactivate such apparatus. Few controlled experiments have been conducted to substantiate this. Cephalopod ink is nonetheless generally thought to be more sophisticated than a simple "smoke screen"; the ink of a number of squid and cuttlefish has been shown to function as a conspecific
chemical alarm.
Physical properties
''
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suspension composed by spheric particles with a size between 80 and 150 nm (measured by
). The particles have a density of , which may be due to the amount of metals that the ink has in its composition (4.7% in weight).
''
'' is a cephalopod species known for releasing luminous ink. The light comes from a substance produced by a dedicated organ before being transferred into the ink sac.
Cephalopod ink contains a number of chemicals in a variety of different concentrations, depending on the species. However, its main constituents are
.
.
'', is associated with the brown colour of cuttlefish ink (for more information, see
''. For this purpose it is generally obtainable from
and Spain. The ink is extracted from the ink sacs during preparation of the dead cephalopod, usually cuttlefish, and therefore contains no mucus. While it is not commonly used in China, cephalopod ink is sometimes used to dye the dough of
.
It is being researched in mice for its antitumor activity against Meth-A fibrosarcoma. It currently remains unclear however if any of the antitumor activity of squid ink can be obtained from oral consumption, and this is indicated as an area for future investigation.