Editing Squid (section)

===Digestive system===
[[File:Chtenopteryx sicula2.jpg|thumb|left|upright=1.1<!--format for low image-->|Ventral view of the viscera of a female ''[[Chtenopteryx sicula]]''|alt=Diagram labeling siphon, intestine, nidamental gland, accessory nidamental gland, renal pore, and branchial heart]]

Like all cephalopods, squids are predators and have complex digestive systems. The mouth is equipped with a sharp, horny [[Cephalopod beak|beak]] mainly made of chitin and [[cross-link]]ed proteins,<ref name="Tan Hoon Guerette Wei pp. 488–495">{{cite journal | last1=Tan | first1=YerPeng | last2=Hoon | first2=Shawn | last3=Guerette | first3=Paul A. | last4=Wei | first4=Wei | last5=Ghadban | first5=Ali | last6=Hao | first6=Cai | last7=Miserez | first7=Ali | last8=Waite | first8=J. Herbert | title=Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient | journal=Nature Chemical Biology | volume=11 | issue=7 | year=2015  | doi=10.1038/nchembio.1833 | pmid=26053298 | pages=488–495 | s2cid=205303026 |quote=the beak contains two protein families. One family consists of chitin-binding proteins (DgCBPs) that physically join chitin chains, whereas the other family comprises highly modular histidine-rich proteins (DgHBPs).| url=http://www.escholarship.org/uc/item/3f21p9m3 }}</ref> which is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain minerals, unlike the teeth and jaws of many other organisms; the cross-linked proteins are histidine- and glycine-rich and give the beak a stiffness and hardness greater than most equivalent synthetic organic materials.<ref>{{cite journal |last1=Miserez |first1=A. |last2=Li |first2=Y. |last3=Waite |first3=H. |last4=Zok |first4=F. |year=2007 |title=Jumbo squid beaks: Inspiration for design of robust organic composites |journal=[[Acta Biomaterialia]] |volume=3 |issue=1 |pages=139–149 |doi=10.1016/j.actbio.2006.09.004 |pmid=17113369}}</ref> The stomachs of captured whales often have indigestible squid beaks inside. The mouth contains the [[radula]], the rough tongue common to all [[Mollusca|molluscs]] except [[bivalvia]], which is equipped with multiple rows of teeth.<ref name=Ruppert/> In some species, toxic [[saliva]] helps to control large prey; when subdued, the food can be torn in pieces by the beak, moved to the oesophagus by the radula, and swallowed.<ref>{{cite book |author1=Hanlon, Roger T. |author2=Messenger, John B. |title=Cephalopod Behaviour |url=https://books.google.com/books?id=Nxfv6xZZ6WYC&pg=PA48 |year=1998 |publisher=Cambridge University Press |isbn=978-0-521-64583-6 |page=48}}</ref>

The food [[bolus (digestion)|bolus]] is moved along the gut by waves of muscular contractions ([[peristalsis]]). The long oesophagus leads to a muscular [[stomach]] roughly in the middle of the visceral mass. The [[Hepatopancreas|digestive gland]], which is equivalent to a vertebrate liver, diverticulates here, as does the [[pancreas]], and both of these empty into the [[Cecum|caecum]], a pouch-shaped sac where most of the absorption of nutrients takes place.<ref name=Ruppert/> Indigestible food can be passed directly from the stomach to the [[rectum]] where it joins the flow from the caecum and is voided through the [[anus]] into the mantle cavity.<ref name=Ruppert/> Cephalopods are short-lived, and in mature squid, priority is given to reproduction;<ref>{{cite news |title=Octopuses and the Puzzle of Aging |author=Godfrey-Smith, Peter |author-link=Peter Godfrey-Smith |url=https://www.nytimes.com/2016/12/02/opinion/sunday/octopuses-and-the-puzzle-of-aging.html |newspaper=[[The New York Times]] |date=2 December 2016 |access-date=12 December 2018}}</ref> the female ''[[Onychoteuthis banksii]]'' for example, sheds its feeding tentacles on reaching maturity, and becomes flaccid and weak after spawning.<ref>{{cite iucn |author=Barratt, I. |author2=Allcock, L. |year=2014 |title=''Onychoteuthis banksii'' |volume=2014 |page=e.T163375A1003448 |doi=10.2305/IUCN.UK.2014-1.RLTS.T163375A1003448.en |access-date=28 April 2025}}</ref><ref>{{cite journal |author=Bolstad, K. S. |year=2008 |title=Two New Species and a Review of the Squid Genus ''Onychoteuthis'' Lichtenstein, 1818 (Oegopsida: Onychoteuthidae) from the Pacific Ocean |journal=Bulletin of Marine Science |volume=83 |issue=3 |pages=481–529 |url=https://www.ingentaconnect.com/content/umrsmas/bullmar/2008/00000083/00000003/art00005 }}</ref>