Editing Giant squid (section)

== Morphology and anatomy ==
{{see also|Squid|Cephalopod}}
{{More citations needed section|date=September 2020}}

Like all squid, a giant squid has a [[Mantle (mollusc)|mantle]] (torso), eight [[cephalopod limb|arms]], and two longer [[cephalopod limb|tentacles]] (the longest known tentacles of any cephalopod). The arms and tentacles account for much of the squid's great length, making it much lighter than its chief predator, the [[sperm whale]]. Scientifically documented specimens have masses of hundreds, rather than thousands, of kilograms.{{citation needed|date=September 2020}}

[[File:Giant squid tentacle club.jpg|left|thumb|Tentacular club of ''Architeuthis'']]
The inside surfaces of the arms and tentacles are lined with hundreds of subspherical [[suction]] cups, {{convert|2|to|5|cm|in|frac=4|abbr=on}} in [[diameter]], each mounted on a stalk. The [[circumference]] of these suckers is lined with sharp, finely serrated rings of [[chitin]].<ref>{{cite journal |author=Roeleveld, M.A.C. |year=2002 |title=Tentacle morphology of the giant squid ''Architeuthis'' from the North Atlantic and Pacific Oceans |journal=Bulletin of Marine Science |volume=71 |issue=2 |pages=725–737 |url=http://www.ingentaconnect.com/content/umrsmas/bullmar/2002/00000071/00000002/art00012 |access-date=9 September 2013 |archive-date=8 March 2016 |archive-url=https://web.archive.org/web/20160308112953/http://www.ingentaconnect.com/content/umrsmas/bullmar/2002/00000071/00000002/art00012 |url-status=live }}</ref> The perforation of these teeth and the suction of the cups serve to attach the squid to its prey. It is common to find circular scars from the suckers on or close to the head of sperm whales that have attacked giant squid.<ref>{{Cite web |title=Giant Squid Sucker Marks {{!}} Smithsonian Ocean |url=https://ocean.si.edu/ocean-life/invertebrates/giant-squid-sucker-marks |access-date=2023-11-23 |website=ocean.si.edu|archive-date=23 November 2023 |archive-url=https://web.archive.org/web/20231123030857/https://ocean.si.edu/ocean-life/invertebrates/giant-squid-sucker-marks |url-status=live }}</ref>

Each [[Cephalopod limb|tentacular club]] is divided into three regions—the [[Carpal bones|carpus]] ("wrist"), [[Manus (anatomy)|manus]] ("hand") and [[dactylus]] ("finger").<ref>{{cite web |author1=Young, R.E. |author2=Vecchione, M. |author3=Mangold, K.M. |year=2001 |url=http://tolweb.org/accessory/Tentacular_Club_Variation_in_Cephalopods?acc_id=2145 |title=Tentacular club variation in cephalopods |website=Tree of Life web project |access-date=16 July 2007 |archive-date=30 September 2007 |archive-url=https://web.archive.org/web/20070930220446/http://tolweb.org/accessory/Tentacular_Club_Variation_in_Cephalopods?acc_id=2145 |url-status=live }}</ref><ref>{{cite web |author1=Young, R.E. |author2=Vecchione, M. |author3=Mangold, K.M. |year=2000 |url=http://tolweb.org/accessory/Cephalopod_Tentacle_Terminology?acc_id=1962 |title=Cephalopod tentacle terminology |website=Tree of Life web project |access-date=16 July 2007 |archive-date=22 May 2013 |archive-url=https://web.archive.org/web/20130522025745/http://tolweb.org/accessory/Cephalopod_Tentacle_Terminology?acc_id=1962 |url-status=live }}</ref> The carpus has a dense cluster of cups, in six or seven irregular, transverse rows. The manus is broader, closer to the end of the club, and has enlarged suckers in two medial rows. The dactylus is the tip. The bases of all the arms and tentacles are arranged in a circle surrounding the animal's single, parrot-like beak, as in other cephalopods.{{citation needed|date=September 2020}}

[[File:A piece of sperm whale skin with Giant Squid sucker scars.JPG|thumb|left|upright|A portion of [[sperm whale]] skin with giant squid sucker scars]]
Giant squid have small [[cephalopod fin|fins]] at the rear of their mantles used for locomotion. Like other cephalopods, they move through [[jet propulsion|jet]] propulsion—by pulling water into the mantle cavity, and pushing it through the [[Siphon (mollusc)|siphon]], in gentle, rhythmic pulses. They can also move quickly by expanding the cavity to fill it with water, then contracting muscles to jet water through the siphon. Giant squid breathe using two large [[Ctenidium (mollusc)|gills]] inside the mantle cavity. The circulatory system is closed, which is a distinct characteristic of cephalopods. Like other squid, they contain dark [[Cephalopod ink|ink]].<ref>{{Cite web |last=Vaughan |first=Jerrod |editor-last=Fabritius |editor-first=Stephanie |title=Architeuthis dux |url=https://animaldiversity.org/accounts/Architeuthis_dux/ |access-date=2023-02-20 |website=Animal Diversity Web|archive-date=22 September 2019 |archive-url=https://web.archive.org/web/20190922175206/https://animaldiversity.org/accounts/Architeuthis_dux/ |url-status=live }}</ref>

[[File:Squid beak measuring.jpg|thumb|upright|The beak of a giant squid, surrounded by the [[Digestive system of gastropods|buccal mass]]]]

The giant squid has a sophisticated [[nervous system]] and complex brain, attracting great interest from scientists. It also has the largest [[cephalopod eye|eyes]] of any living creature except perhaps the [[colossal squid]]—up to at least {{convert|27|cm|abbr=on}} in diameter, with a {{convert|9|cm|in|frac=2|abbr=on}} pupil (only the extinct [[ichthyosaur]]s are known to have had larger eyes).<ref name=Nilsson2012>{{cite journal |doi=10.1016/j.cub.2012.02.031 |title=A unique advantage for giant eyes in Giant Squid |year=2012 |last1=Nilsson |first1=Dan-Eric |last2=Warrant |first2=Eric J. |last3=Johnsen |first3=Sönke |last4=Hanlon |first4=Roger |last5=Shashar |first5=Nadav |journal=Current Biology |volume=22 |issue=8 |pages=683–688 |pmid=22425154|doi-access=free |bibcode=2012CBio...22..683N }}</ref> Large eyes can better detect light (including [[bioluminescence|bioluminescent]] light), which is scarce in deep water. The giant squid probably cannot see color, but it can probably discern small differences in tone, which is important in the low-light conditions of the deep ocean.<ref>{{cite book |author=Piper, R. |year=2007 |title=Extraordinary Animals: An encyclopedia of curious and unusual animals |publisher=Greenwood Press}}</ref>

Giant squid and some other large squid species maintain neutral [[buoyancy]] in [[seawater]] through an [[ammonium chloride]] solution which is found throughout their bodies and is lighter than seawater. This differs from the method of flotation used by most fish, which involves a gas-filled [[swim bladder]]. The solution tastes somewhat like [[Salty liquorice|salty liquorice/salmiak]] and makes giant squid unattractive for general human consumption.<ref>{{Cite web |date=2022-05-01 |title=Everything you need to know about giant squids |url=https://www.aquarium.co.za/news/everything-you-need-to-know-about-giant-squids |access-date=2025-05-13 |website=Two Oceans Aquarium |language=en}}</ref>

Like all [[cephalopod]]s, giant squid use organs called [[statocyst]]s to sense their orientation and motion in water. The age of a giant squid can be determined by "growth rings" in the statocyst's [[statocyst|statolith]], similar to determining the age of a tree by counting its rings. Much of what is known about giant squid age is based on estimates of the growth rings and from undigested beaks found in the [[stomach]]s of sperm whales.{{citation needed|date=September 2020}}