Squid
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{{otheruses}}
{{Taxobox
| name = Squid
| image = Mastigoteuthis flammea.jpg
| image_width = 220px
| image_caption = ''[[Mastigoteuthis flammea]]''<br>A species of [[whip-lash squid]]
| regnum = [[Animal]]ia
| phylum = [[Mollusk|Mollusca]]
| classis = [[Cephalopod]]a
| subclassis = [[Coleoidea]]
| superordo = [[Decapodiformes]]
| ordo = '''Teuthida'''
| ordo_authority = [[Adolf Naef|A. Naef]], 1916b
| subdivision_ranks = [[Suborders]]
| subdivision =
†[[Plesioteuthididae]] <small>(''[[incertae sedis]]'')</small><br>
[[Myopsina]]<br>
[[Oegopsina]]
}}
'''Squid''' are a large, diverse group of marine [[cephalopod]]s. Like all cephalopods, squid are distinguished by having a distinct head, bilateral symmetry, a [[mantle (mollusc)|mantle]], and [[cephalopod arm|arm]]s. Squid, like [[cuttlefish]], have eight arms and two tentacles arranged in pairs.
==Modification from ancestral forms==
Squid have differentiated from their ancestral [[mollusk]]s in such a way that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What before may have been the [[foot]] of the ancestor is now modified into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of [[vertebrate]]s.
The shell of the ancestor has been lost, with only an internal gladius, or pen, remaining.
==Anatomy==
[[Image:Loligo vulgaris.jpg|250px|thumb|[[European Squid]] (''Loligo vulgaris'')]]
The main body mass of the squid is enclosed in the [[mantle (mollusc)|mantle]], which has a swimming fin along each side. It should be noted that these fins, unlike in other marine organisms, are not the main source of ambulation in most species. The skin of the squid is covered in [[chromatophore]]s, which enable the squid to change color to suit its surroundings. The underside of the squid is also found to be lighter than the topside, in order to provide [[camouflage]] from both prey and predator.
Under the body are openings to the mantle cavity, which contains the [[gills]] (ctenidia) and openings to the excretory and [[reproductive system]]s. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion via precise [[jet propulsion]]. This is done by sucking water into the mantle cavity and quickly expelling it out of the siphon in a fast, strong jet. The direction of the siphon can be changed in order to suit the direction of travel.
Inside the mantle cavity, beyond the siphon, lies the visceral mass of the squid, which is covered by a thin, membranous [[Squamous epithelium|epidermis]]. Under this are all the major internal organs of the squid.
===Nervous system===
The [[Squid giant axon|giant axon]] of the squid, which may be up to 1 mm in diameter, [[nerve|innervates]] the mantle and controls part of the jet propulsion system.
===Reproductive system===
[[Image:Chtenopteryx sicula2.jpg|250px|thumb|Ventral view of the viscera of ''[[Chtenopteryx sicula]]''.]]
In female squid, the [[ink sac]] is hidden from view by a pair of white [[nidamental gland]]s, which lie anterior to the gills. There are also red-spotted accessory nidamental glands. Both of these organs are associated with manufacture of food supplies and shells for the eggs. Females also have a large translucent [[ovary]], situated towards the posterior of the visceral mass.
Male squid do not possess these organs, but instead have a large [[testis]] in place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain [[spermatophore]]s, which are placed inside the mantle of the female during mating.
===Digestive system===
Squid, like all cephalopods, have complex digestive systems. Food is transported into a muscular [[stomach]], found roughly in the midpoint of the visceral mass. The bolus is then transported into the [[caecum]] 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 and so the stomach and caecum often shrivel up during the later stages of life. Finally, food goes to the [[liver]] (or digestive gland), found at the siphon end of the squid, for absorption. Solid waste is passed out of the [[rectum]]. Beside the rectum is the ink sac, which allows a squid to discharge a black ink into the mantle cavity at short notice.
===Cardiovascular system===
Squid have three [[heart]]s. Two [[branchial heart]]s, feeding the gills, each surrounding the larger systemic heart that pumps blood around the body. The hearts have a faint greenish appearance and are surrounded by the renal sacs - the main excretory system of the squid. The [[kidney]]s are faint and 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 [[ventricle]] and two upper [[auricle]]s.
===Head===
The head end of the squid bears 8 arms and 2 tentacles, each a form of [[muscular hydrostat]] containing many suckers along the edge. These tentacles do not grow back if severed. In the mature male squid, one basal half of the left ventral tentacle is [[hectocotylus|hectocotylised]] — and ends in a copulatory pad rather than suckers. It is used for intercourse between mature males and females.
The mouth of the squid is equipped with a sharp horny beak mainly made of [[chitin]] <ref>{{cite book |last=Clarke |first=M.R. |authorlink= |coauthors= |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 [[proteins]], and is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species.<ref>{{cite journal |last=Miserez|first=A |authorlink= |coauthors=Li, Y; Waite, H; Zok, F |year=2007 |month= |title=Jumbo squid beaks: Inspiration for design of robust organic composites |journal=Acta Biomaterialia |volume=3 |issue= |pages=139–149 |id= |url= |accessdate= |quote=|doi=10.1016/j.actbio.2006.09.004 }}</ref>
Captured [[whale]]s often have squid beaks in their stomachs, the beak being the only indigestible part of the squid. The mouth contains the [[radula]] (the rough tongue common to all [[mollusc]]s except [[bivalvia]] and [[aplacophora]]).
The eyes, found on either side of the head, each contain a hard [[Lens (anatomy)|lens]]. The lens is focused by moving, much like the lens of a [[camera]] or [[telescope]], rather than changing shape like a [[human eye]].
[[Image:Giant squid melb aquarium03.jpg|thumb|350px|[[Giant squid]] in [[Melbourne Aquarium]]]]
===Size===
{{seealso|Giant squid|Colossal Squid|Cephalopod size}}
The majority of squid are no more than 60 cm long, although the [[giant squid]] may reach 13 m in length.<ref name=OShea>O'Shea, S. 2003. [http://www.tonmo.com/science/public/giantsquidfacts.php "Giant Squid and Colossal Squid Fact Sheet".] The Octopus News Magazine Online.</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=[http://www.journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=219642 A Geographical Information System (GIS) Atlas of cephalopod distribution in the Southern Ocean.]}} ''Antarctic Science'' '''11''':61-62. [http://www.nerc-bas.ac.uk/public/mlsd/squid-atlas/ online version]</ref> but poorly understood species, ''Mesonychoteuthis hamiltoni'' (the [[Colossal Squid]]), was discovered. This species may grow to 14 m in length, making it the largest [[invertebrate]].<ref>Anderton, H.J. 2007. [http://www.beehive.govt.nz/ViewDocument.aspx?DocumentID=28451 Amazing specimen of world's largest squid in NZ]. New Zealand Government website.</ref> It also possesses the largest eyes in the animal kingdom. Giant squid are often featured in literature and folklore with a frightening connotation. The [[Kraken]] is a legendary tentacled monster possibly based on sightings of real giant squid.
In February 2007, a Colossal Squid weighing 495 kg (1,091 lb) and measuring around 10 metres (33 ft) in length was caught by a New Zealand fishing vessel off the coast of Antarctica. In July 2008 another giant squid (25 feet long) was found dead floating off the California coast.<ref>[http://news.bbc.co.uk/2/hi/asia-pacific/6478801.stm Microwave plan for colossal squid]. [[BBC]] News [[March 22]], [[2007]].</ref>
==Classification==
[[Image:6742 aquaimages.jpg|thumb|250px|[[Caribbean Reef Squid]], [[Bonaire]].]]
Squid are members of the class [[Cephalopod]]a, subclass [[Coleoidea]], order '''Teuthida''', of which there are two major suborders, [[Myopsina]] and [[Oegopsina]] (including the [[giant squid]]s like ''Architeuthis dux''). Teuthida is the largest of the cephalopod orders, edging out the [[octopus]]es (order Octopoda) for total number of [[species]], with 298 classified into 28 families.
The order Teuthida is a member of the superorder [[Decapodiformes]] (from the [[Greek language|Greek]] for "ten legs"). Two other orders of decapodiform cephalopods are also called squid, although they are [[taxonomy|taxonomically]] distinct from Teuthida and differ recognizably in their gross anatomical features. They are the [[bobtail squid]] of order [[Sepiolida]] and the [[Ram's Horn Squid]] of the monotypic order [[Spirulida]]. The [[Vampire Squid]], however, is more closely related to the octopuses than to any of the squid.
*'''CLASS [[Cephalopoda|CEPHALOPODA]]'''
**Subclass [[Nautiloidea]]: nautilus
**Subclass [[Coleoidea]]: squid, [[octopus]], [[cuttlefish]]
***Superorder [[Octopodiformes]]
***Superorder [[Decapodiformes]]
****?Order †[[Boletzkyida]]
****Order [[Spirulida]]: Ram's Horn Squid
****Order [[Sepiida]]: cuttlefish
****Order [[Sepiolida]]: bobtail squid
****'''Order Teuthida''': squid
*****Family †[[Plesioteuthididae]] <small>(''[[incertae sedis]]'')</small>
*****Suborder [[Myopsina]]
******Family [[Australiteuthidae]]
******Family [[Loliginidae]]: inshore, [[calamari]], and grass squid
*****Suborder [[Oegopsina]]
******Family [[Sharpear Enope Squid|Ancistrocheiridae]]: Sharpear Enope Squid
******Family [[Architeuthis|Architeuthidae]]: giant squid
******Family [[Bathyteuthis|Bathyteuthidae]]
******Family [[Bush-club Squid|Batoteuthidae]]: Bush-club Squid
******Family [[Brachioteuthis|Brachioteuthidae]]
******Family [[Chiroteuthidae]]
******Family [[Chtenopteryx|Chtenopterygidae]]: comb-finned squid
******Family [[glass squid|Cranchiidae]]: glass squid
******Family [[Cycloteuthidae]]
******Family [[Enoploteuthidae]]
******Family [[Gonatidae]]: armhook squid
******Family [[Histioteuthis|Histioteuthidae]]: jewel squid
******Family [[Joubin's Squid|Joubiniteuthidae]]: Joubin's Squid
******Family [[Grimaldi Scaled Squid|Lepidoteuthidae]]: Grimaldi Scaled Squid
******Family [[Lycoteuthidae]]
******Family [[bigfin squid|Magnapinnidae]]: bigfin squid
******Family [[Mastigoteuthidae]]: whip-lash squid
******Family [[Neoteuthidae]]
******Family [[Octopoteuthidae]]
******Family [[Ommastrephidae]]: flying squid
******Family [[Onychoteuthidae]]: hooked squid
******Family [[Pholidoteuthis|Pholidoteuthidae]]
******Family [[Promachoteuthis|Promachoteuthidae]]
******Family [[Glacial Squid|Psychroteuthidae]]: Glacial Squid
******Family [[Pyroteuthidae]]: fire squid
******Family [[Thysanoteuthis|Thysanoteuthidae]]: rhomboid squid
******Family [[Walvisteuthis|Walvisteuthidae]]
******''[[Parateuthis tunicata]]'' <small>(''[[incertae sedis]]'')</small>
==As food==
{{main|squid (food)}}
[[Image:Fried calamari.jpg|thumb|200px|Fried [[calamari]]: breaded, [[deep frying|deep-fried]] squid]]
Many species of squid are popular as food in cuisines as diverse as [[Korean cuisine|Korean]] and [[Italian cuisine|Italian]]. In [[English language|English]]-speaking countries, it is often known by the name ''[[calamari]]''. Individual species of squid are found abundantly in certain areas and provide large catches for [[fishery|fisheries]]. 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 of the squid that are not eaten are its beak and gladius (pen).
==In popular culture==
{{see also|Giant squid in popular culture}}
[[Image:Fried baby squid.jpg|thumb|200px|Fried baby squid is a dish commonly associated with [[Chinese cuisine]].]]
The [[giant squid]] is featured in [[Jules Verne]]'s ''[[Twenty Thousand Leagues Under the Sea]]'', in which one attacks [[Captain Nemo]]'s ship, the ''[[Nautilus (Verne)|Nautilus]]''. It is also featured in the [[Harry Potter]] series, where it is friendly rather than dangerous.
==References==
{{reflist}}
== External links ==
{{Commons|Teuthida|Squid}}
{{cookbook}}
*[http://www.cephbase.utmb.edu/spdb/squid.cfm CephBase: Teuthida]
*[http://www.tepapa.govt.nz/TePapa/English/CollectionsAndResearch/CollectionAreas/NaturalEnvironment/Molluscs/ColossalSquid/ Colossal Squid at the Museum of New Zealand Te Papa Tongarewa]
*[http://www.rogerbly.com/video/squid Market squid mating, laying eggs (video)]
*[http://www.sciam.com/article.cfm?chanID=sa003&articleID=00030326-0783-133B-878383414B7F0000 Scientific American - Giant Squid]
*[http://www.thecephalopodpage.org The Cephalopod Page]
*[http://www.tonmo.com The Octopus News Magazine Online]
[[Category:Squid| ]]
[[Category:Edible molluscs]]
[[Category:Commercial molluscs]]
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