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{{Two other uses|cephalopods|the web proxy|Squid (software)}}
{{Redirect|Squids|the video game|Squids (video game)}}

{{pp-move|small=yes}}
{{Automatic taxobox
| taxon = Teuthida
| fossil_range = (at least) {{fossil range|Late Cretaceous|Recent|ref=<ref name=Tanabe2006>{{Cite journal
| last1 = Tanabe | first1 = K.
| last2 = Hikida | first2 = Y.
| last3 = Iba | first3 = Y.
| year = 2006
| title = Two Coleoid Jaws from the Upper Cretaceous of Hokkaido, Japan
| journal = Journal of Paleontology
| volume = 80
| issue = 1
| pages = 138–145
| doi = 10.1666/0022-3360(2006)0802.0.CO;2
| postscript = <!--None-->
}}</ref>}}
| image =Loligo vulgaris.jpg
| image_caption = ] (''Loligo vulgaris'')
| alt=Photo of squid with 8 short arms and two longer tentacles
| authority = ], 1916
| subdivision_ranks = ]
| subdivision =
†] <small>('']'')</small><br>
]<br>
]
}}

'''Squid''' are ]s of the ] '''Teuthida''', which comprises around 304 species.<ref>http://marinespecies.org/aphia.php?p=browser&id=325342&expand=true#ct</ref> Like all other cephalopods, squid have a distinct head, ], a ], and ]. Squid, like ], have eight ] arranged in pairs and two, usually longer, ]s. Squid are strong swimmers and certain species can "fly" for short distances out of the water.<ref>Jabr, F. 2010. ''Scientific American'', August 2, 2010.</ref>

==Modification from ancestral forms==
]'' from the ] of ], France]]
Squid have differentiated from their ancestral ]s such that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What before may have been the ] of the ancestor is modified into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of ]s.

The ancestral shell has been lost, with only an internal ], or pen, remaining. The pen is a feather-shaped internal structure that supports the squid's ] and serves as a site for muscle attachment. It is made of a ]-like material.

==Introduction==

]
The main body mass is enclosed in the ], which has a ] along each side. These fins, unlike in other marine organisms, are not the main source of locomotion in most species.

The skin is covered in ]s, which enable the squid to change color to suit its surroundings, making it practically ]. The underside is also almost always lighter than the topside, to provide ] from both prey and predator.

Under the body are openings to the mantle cavity, which contains the ] (ctenidia) and openings to the excretory and ]s. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion via precise ].<ref name=Johnson1972>{{Cite journal
| last1 = Johnson | first1 = W.
| last2 = Soden | first2 = P.D.
| last3 = Trueman | first3 = E.R.
| year = 1972
| title = A Study in Jet Propulsion: An analysis of the motion of the squid, ''Loligo vulgaris''
| journal = Journal of Experimental Biology
| volume = 56
| issue = 1
| pages = 155–165
| postscript = <!--None-->
}}</ref> In this form of locomotion, water is sucked into the mantle cavity and expelled out of the siphon in a fast, strong jet. The direction of the siphon can be changed, to suit the direction of travel.

Inside the mantle cavity, beyond the siphon, lies the visceral mass, which is covered by a thin, membranous ]. Under this are all the major internal organs.

===Nervous system===
The ], which may be up to 1&nbsp;mm (0.04&nbsp;in) in diameter in some larger species, ] the mantle and controls part of the jet propulsion system.

As cephalopods, squid exhibit relatively high intelligence among invertebrates. For example, groups of ] hunt cooperatively, using active communication. (See ].)

===Reproductive system===
{{multiple image
|direction=vertical
|width=220
|image1= Onykia ingens with non-erect penis.jpg
|caption1= A dissected male specimen of '']'', showing a nonerect penis (the white tubular structure located below most of the other organs)
|image2= Onykia ingens with erect penis.jpg
|caption2= A specimen of the same species exhibiting elongation of the penis to 67&nbsp;cm
}}
In females, the ] is hidden from view by a pair of white ]s, which lie anterior to the gills. Also, red-spotted accessory nidamental glands are present. Both organs are associated with nutrient manufacture and shells for the eggs. Females also have a large translucent ], situated towards the posterior of the visceral mass.

Males do not possess these organs, but instead have a large ] in place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain ]s, which are placed inside the female's mantle during mating.

Shallow-water species of the ] and ]/] zones are characterised by the presence of ], specially modified arms used to fertilise the female's eggs.<ref name=penis>Arkhipkin, A.I. & V.V. Laptikhovsky 2010. Observation of penis elongation in ''Onykia ingens'': implications for spermatophore transfer in deep-water squid. ''Journal Molluscan Studies'', published online on June 30, 2010. {{DOI|10.1093/mollus/eyq019}}</ref> Most deep-sea squid lack hectocotyli and have longer penises; ] and ] are exceptions.<ref name=penis /> ] of the genus ''Architeuthis'' are unusual in that they possess both a large penis and modified arm tips, although whether the latter are used for spermatophore transfer is uncertain.<ref name=penis /> Penis elongation has been observed in the deep-water species '']''; when erect, the penis may be as long as the mantle, head, and arms combined.<ref name=penis /><ref>Walker, M. 2010. . ''BBC Earth News'', July 7, 2010.</ref> As such, deep-water squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile ]s.<ref name=penis />

===Digestive system===
Like all cephalopods, squid have complex digestive systems. The muscular ] is found roughly in the midpoint of the visceral mass. From there, the ] moves into the ] for digestion. The caecum, a long, white organ, is found next to the ovary or testis. In mature squid, more priority is given to reproduction such that the stomach and caecum often shrivel up during the later life stages. Finally, food goes to the ] (or digestive gland), found at the siphon end, for absorption. Solid waste is passed out of the ]. Beside the rectum is the ink sac, which allows a squid to rapidly discharge black ink into the mantle cavity.

]''|alt=Diagram labeling siphon, intestine, nidamental gland, accessory nidamental gland, renal pore, and branchial heart.]]

===Cardiovascular system===
Squid have three ]s. Two ]s feed the gills, each surrounding the larger systemic heart that pumps blood around the body. Squid blood contains the ]-rich ] ] for transporting ]. The faintly greenish hearts are surrounded by the renal sacs - the main excretory system. The ]s are difficult to identify and stretch from the hearts (located at the posterior side of the ink sac) to the liver. The systemic heart is made of three chambers, a lower ] and two upper ].

===Head===
The head end bears eight arms and two tentacles, each a form of ] containing many suckers along the edge. These tentacles do not grow back if severed. In the mature male, one basal half of the left ventral tentacle is ] — and ends in a copulatory pad rather than suckers. It is used for sexual intercourse.

The mouth is equipped with a sharp, horny ] mainly made of ]<ref>
{{cite book
|last=Clarke |first=M.R.
|authorlink=
|title=A Handbook for the Identification of Cephalopod Beaks
|year=1986
|publisher=Clarendon Press
|location=Oxford
|isbn=0-19-857603-X
}}</ref> and cross-linked ], and 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, including marine species.<ref>
{{cite journal
|last=Miserez|first=A
|authorlink=
|author2=Li, Y |author3=Waite, H |author4= Zok, F
|year=2007
|title=Jumbo squid beaks: Inspiration for design of robust organic composites
|journal=]
|volume=3
|issue=1
|pages=139–149
|quote=
|doi=10.1016/j.actbio.2006.09.004
|pmid=17113369
}}</ref>
Captured ]s often have indigestible squid beaks in their stomachs. The mouth contains the ] (the rough tongue common to all ]s except ]).

The eyes, on either side of the head, each contain a hard ]. The image is focused by changing the position of the lens, as in a ] or ], rather than changing the shape of the lens, as in the ].

Squid appear to have limited hearing.<ref>{{cite news|url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8095000/8095977.stm|title=The cephalopods can hear you |publisher=BBC|date=15 June 2009|author=Matt Walker|accessdate = 2010-04-02}}</ref>

===Size===
] in ]|alt=Photo of squid with prominiently visible eye]]
{{see also|Giant squid|Colossal squid|Cephalopod size}}
The majority are no more than {{convert|60|cm|in|abbr=on}} long, although the ] may reach {{convert|13|m|ft|abbr=on}}.<ref name=OShea>
{{cite web
|last=O'Shea |first=S.
|year=2003
|url=http://www.tonmo.com/science/public/giantsquidfacts.php
|title=Giant Squid and Colossal Squid Fact Sheet
|publisher=The Octopus News Magazine Online.
}}</ref>

In 1978, sharp, curved claws on the suction cups of squid tentacles cut up the rubber coating on the hull of the ]. The size suggested the largest squid known at the time.<ref name="proceedings">Johnson, C. Scott "Sea Creatures and the Problem of Equipment Damage" ''United States Naval Institute Proceedings'' August 1978 pp.106-107</ref>

In 2003, a large specimen of an abundant<ref>Xavier, J.C., P.G. Rodhouse, P.N. Trathan & A.G. Wood 1999. {{PDF|1=}} ''Antarctic Science'' '''11''':61-62. </ref> but poorly understood species, ''Mesonychoteuthis hamiltoni'' (the ]), was discovered. This species may grow to {{convert|14|m|ft|abbr=on}} in length, making it the largest ].<ref>
{{cite web
|last=Anderton |first=Jim
|date=22 February 2007
|url=http://www.beehive.govt.nz/release/world039s-largest-squid-landed-nz
|title=World's largest squid landed in NZ
|publisher=New Zealand Government website
}}</ref> Squid have the largest eyes in the animal kingdom. The ] is a legendary tentacled monster possibly based on sightings of real giant squid.

In February&nbsp;2007, a New Zealand fishing vessel caught a ] weighing {{convert|495|kg|lb|abbr=on}} and measuring around {{convert|10|m|ft|abbr=on}} off the coast of Antarctica.<ref>
{{cite news
|url=http://news.bbc.co.uk/2/hi/asia-pacific/6478801.stm
|title=Microwave plan for colossal squid
|publisher=BBC News
|date=March 22, 2007
}}</ref> This specimen represents the largest cephalopod to ever be scientifically documented.

==Classification==
]'']]
]'']]
]'']]
]'']]
]'']]
]'']]
Squid are members of the class ]a, subclass ], order '''Teuthida''', which has two major suborders, ] and ] (including ]s such as ''Architeuthis dux''). Teuthida is the largest cephalopod order with around 300 species classified into 29 families.

The order Teuthida is a member of the superorder ] (from the ] for "ten legs"). Two other orders of decapodiform cephalopods are also called squid, although they are ] distinct from Teuthida and differ recognizably in their gross anatomical features. They are the ] of order ] and the ] of the monotypic order ]. The ], however, is more closely related to the octopuses than to any squid.
* '''CLASS ]'''
** Subclass ]: nautilus
** Subclass ]: squid, ], ]
*** Superorder ]
*** Superorder ]
**** ?Order †]
**** Order ]: ram's horn squid
**** Order ]: cuttlefish
**** Order ]: bobtail squid
**** '''Order Teuthida''': squid
***** Family †] <small>('']'')</small>
***** Suborder ]
****** Family ]
****** Family ]: inshore, ], and grass squid
***** Suborder ]
****** Family ]: sharpear enope squid
****** Family ]: ]
****** Family ]
****** Family ]: bush-club squid
****** Family ]
****** Family ]
****** Family ]: comb-finned squid
****** Family ]: glass squid
****** Family ]
****** Family ]
****** Family ]: armhook squid
****** Family ]: jewel squid
****** Family ]: Joubin's squid
****** Family ]: Grimaldi scaled squid
****** Family ]
****** Family ]: bigfin squid
****** Family ]: whip-lash squid
****** Family ]
****** Family ]
****** Family ]: flying squid
****** Family ]: hooked squid
****** Family ]
****** Family ]
****** Family ]: glacial squid
****** Family ]: fire squid
****** Family ]: rhomboid squid
****** Family ]
****** '']'' <small>('']'')</small>

==Commercial fishing==
According to the ], the cephalopod catch for 2002 was {{convert|3173272|t|lb|sigfig=7}}. Of this, 2,189,206 tonnes, or 75.8 percent, was squid.<ref name="Rodhouse">
{{cite journal
|last=Rodhouse |first=Paul G
|year=2005
|title=Review of the state of world marine fishery resources: Fisheries technical paper
|url=http://www.fao.org/docrep/009/y5852e/Y5852E08.htm#ch3.2
|journal=World squid resources
|publisher= ]
|issue=457
|isbn=92-5-105267-0
}}</ref> The following table lists the squid species fishery catches which exceeded {{convert|10000|t|lb}} in 2002.
{| class="wikitable"
|-
| colspan="5" style="text-align:center; width:480px;"| '''World squid catch in 2002'''<ref name="Rodhouse"/>
|-
! Species
! Family
! Common name
! Catch<br />tonnes
! Percent
|-
| ''Loligo gahi'' or ''Doryteuthis gahi''
| ]
| ]
| 24,976
| 1.1
|-
| ''Loligo pealei''
| ]
| ]
| 16,684
| 0.8
|-
| Common squid nei<ref name="nei">nei: not elsewhere included</ref>
| ]
|
| 225,958
| 10.3
|-
| ''Ommastrephes bartramii''
| ]
| ]
| 22,483
| 1.0
|-
| '']''
| ]
| Argentine shortfin squid
| 511,087
| 23.3
|-
| ''Dosidicus gigas''
| ]
| ]
| 406,356
| 18.6
|-
| ''Todarodes pacificus''
| ]
| ]
| 504,438
| 23.0
|-
| '']''
| ]
| Wellington flying squid
| 62,234
| 2.8
|-
| Squid nei<ref name="nei"/>
| Various
|
| 414,990
| 18.6
|-
| '''Total squid'''
|
|
| 2,189,206
| 100.0
|}

==As food==
{{main|Squid (food)}}
]: breaded, ] squid|alt=Photo of rings of breaded, fried squid]]
Many species are popular as food in cuisines as diverse as ], ], ], ], ], ], ], ], ], ], ], ], ] and ].

In ]-speaking countries, squid as food is often marketed using the Italian word '']''. Squid are found abundantly in certain areas, and provide large catches for ]. The body can be stuffed whole, cut into flat pieces, or sliced into rings. The arms, tentacles, and ink are also edible; in fact, the only parts not eaten are the ] and ] (pen). Squid is a good food source for ] and ], and high in ],<ref>{{Dead link|date=June 2012}}</ref> ], ], and ].<ref></ref>

==See also==
*]
{{Misplaced Pages books|Cephalopoda}}
{{-}}

==References==
{{reflist|2}}

==External links==
{{Commons|Teuthida|Squid}}
{{cookbook}}
*
*
*
*
*
*

{{commercial fish topics}}
{{Edible molluscs}}

]
]
]

Revision as of 01:38, 11 June 2015

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