Editing Cephalopod (section)

===Ink===
{{Main|Cephalopod ink|ink sac}}
With the exception of the [[Nautilidae]] and the species of [[octopus]] belonging to the [[suborder]] [[Cirrina]],<ref>{{cite book |first1=Roger T. |last1=Hanlon |first2=John B. |last2=Messenger|title=Cephalopod Behaviour |page=2 |publisher=Cambridge University Press |year=1999 |isbn=978-0-521-64583-6}}</ref> all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse [[predator]]s.<ref name=Boyle>{{cite book |isbn=978-0-632-06048-1 |first1=Peter |last1=Boyle |first2=Paul |last2=Rodhouse |year=2004 |publisher=Blackwell |url=https://books.google.com/books?id=4UtCi2B4VnoC|doi=10.1002/9780470995310.ch2 |title=Cephalopods: ecology and fisheries }}</ref> This sac is a muscular bag which originated as an extension of the hindgut. It lies beneath the gut and opens into the anus, into which its contents – almost pure [[melanin]] – can be squirted; its proximity to the base of the funnel means the ink can be distributed by ejected water as the cephalopod uses its jet propulsion.<ref name=Boyle/> The ejected cloud of melanin is usually mixed, upon expulsion, with [[mucus]], produced elsewhere in the mantle, and therefore forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator, like a [[smoke screen|smokescreen]]. However, a more sophisticated behavior has been observed, in which the cephalopod releases a cloud, with a greater mucus content, that approximately resembles the cephalopod that released it (this decoy is referred to as a [[Pseudomorph#In other fields|pseudomorph]]). This strategy often results in the predator attacking the pseudomorph, rather than its rapidly departing prey.<ref name=Boyle/> For more information, see [[Cephalopod ink#Inking behaviours|Inking behaviors]].

The ink sac of cephalopods has led to a common name of "inkfish",<ref>{{cite encyclopedia |title=inkfish |url=https://www.merriam-webster.com/dictionary/inkfish |dictionary=Merriam-Webster |access-date=1 February 2018}}</ref> formerly the pen-and-ink fish.<ref>{{cite book |last1=Bickerdyke |first1=John |title=Sea Fishing |date=1895 |publisher=Longmans, Green, and Co. |location=London |page=114 |url=https://archive.org/stream/badmintonlibrar06watsgoog#page/n13/mode/2up/ |quote=the common squid or calamary (''Loligo vulgaris''). It is sometimes called the pen-and-ink fish, on account of its ink bag, and the delicate elongated shell which is found within it.}}</ref>

{{multiple image
|direction = vertical
|align     = right
|width     = 250
|image1    = Chtenopteryx sicula2.jpg
|caption1  = Viscera of ''[[Chtenopteryx sicula]]''
|image2    = Ocythoe tuberculata viscera.jpg
|caption2  = Viscera of ''[[Ocythoe tuberculata]]''
}}