name = Squid
image_width = 220px
image_caption = "
A species of
phylum = Mollusca
ordo = Teuthida
ordo_authority = A. Naef, 1916b
subdivision = †
Plesioteuthididae(" incertae sedis") Myopsina Oegopsina
Squid are marine
cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms and two tentacles arranged in pairs.
Modification from ancestral forms
Squid have differentiated from their ancestral
mollusks in such a way that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What before may have been the footof the ancestor is now modified into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of vertebrates.
The shell of the ancestor has been lost, with only an internal gladius, or pen, remaining. The pen is a feather-shaped internal structure that supports the mantle of squid and serves as a site for muscle attachment. It is made of a
The main body mass of the squid is enclosed in the 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
chromatophores, which enable the squid to change color to suit its surroundings. The underside of the squid is also almost always lighter in color than the topside, in order to provide camouflagefrom 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 systems. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion via precise jet propulsion. 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, 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 epidermis. Under this are all the major internal organs of the squid.
In female squid, the
ink sacis hidden from view by a pair of white nidamental glands, 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
testisin place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain spermatophores, which are placed inside the mantle of the female during mating.
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 caecumfor 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.
Squid have three
hearts. Two branchial hearts, 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 kidneys 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 ventricleand two upper auricles.
The head end of the squid bears 8 arms and 2 tentacles, each a form of
muscular hydrostatcontaining 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 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[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 ] 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. [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 ] Captured whales 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 molluscs except bivalviaand aplacophora).
The eyes, found on either side of the head, each contain a hard lens. The lens is focused through movement, much like the lens of a
cameraor telescope, rather than changing shape as the lens in the human eyedoes.
The majority of squid are no more than convert|60|cm|in long, although the
giant squidmay reach convert|13|m|ft in length.O'Shea, S. 2003. [http://www.tonmo.com/science/public/giantsquidfacts.php "Giant Squid and Colossal Squid Fact Sheet".] The Octopus News Magazine Online.]
In 1978, the "NOFOUL" rubber coating of the
AN/SQS-26 SONARdome of USS Stein (FF-1065)was damaged by multiple cuts over 8 percent of the dome surface. Nearly all of the cuts contained remnants of sharp, curved claws found on the rims of suction cups of some squid tentacles. The claws were much larger than those of any squid that had been discovered at that time.Johnson, C. Scott "Sea Creatures and the Problem of Equipment Damage" "United States Naval Institute Proceedings" August 1978 pp.106-107]
In 2003, a large specimen of an abundant [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] ] but poorly understood species, "Mesonychoteuthis hamiltoni" (the
Colossal Squid), was discovered. This species may grow to convert|14|m|ft in length, making it the largest invertebrate. [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.] It also possesses the largest eyes in the animal kingdom. Giant squid are often featured in literature and folklore with a frightening connotation. The Krakenis 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. [ [http://news.bbc.co.uk/2/hi/asia-pacific/6478801.stm Microwave plan for colossal squid] .
BBCNews March 22, 2007.]
Squid are members of the class
Cephalopoda, subclass Coleoidea, order Teuthida, of which there are two major suborders, Myopsinaand Oegopsina(including the giant squids like "Architeuthis dux"). Teuthida is the largest of the cephalopod orders, edging out the octopuses (order Octopoda) for total number of species, with around 300 classified into 29 families.
The order Teuthida is a member of the superorder
Decapodiformes(from the Greek for "ten legs"). Two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from Teuthida and differ recognizably in their gross anatomical features. They are the bobtail squidof order Sepiolidaand the Ram's Horn Squidof the monotypic order Spirulida. The Vampire Squid, however, is more closely related to the octopuses than to any of the squid.
Coleoidea: squid, octopus, cuttlefish
Spirulida: Ram's Horn Squid
Sepiolida: bobtail squid
****Order Teuthida: squid
Plesioteuthididae(" incertae sedis")
Loliginidae: inshore, calamari, and grass squid
******Family Ancistrocheiridae: Sharpear Enope Squid
******Family Architeuthidae: giant squid
******Family Batoteuthidae: Bush-club Squid
******Family Chtenopterygidae: comb-finned squid
******Family Cranchiidae: glass squid
Gonatidae: armhook squid
******Family Histioteuthidae: jewel squid
******Family Joubiniteuthidae: Joubin's Squid
******Family Lepidoteuthidae: Grimaldi Scaled Squid
******Family Magnapinnidae: bigfin squid
Mastigoteuthidae: whip-lash squid
Ommastrephidae: flying squid
Onychoteuthidae: hooked squid
******Family Psychroteuthidae: Glacial Squid
Pyroteuthidae: fire squid
******Family Thysanoteuthidae: rhomboid squid
Parateuthis tunicata" (" incertae sedis")
According to the
FAO, the total cephalopod catch for 2002 was 3,173,272 tonnes. Of this, 2,189,206 tonnes, or 75.8 percent, was squid.Rodhouse, Paul G (2005) Review of the state of world marine fishery resources: [http://www.fao.org/docrep/009/y5852e/Y5852E08.htm#ch3.2 World squid resources."] FAO: Fisheries technical paper, No 447. ISBN 95-5-105267-0] The following table lists the squid species fishery catches which exceeded 10,000 tonnes in 2002.
In English-speaking countries, squid as food is often known by the Mediterranean (Spanish and Italian) word "
Individual species of squid are found abundantly in certain areas, and provide large catches for fisheries.
The body of squid 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).
* [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]
Wikimedia Foundation. 2010.