Squid Temporal range: (at least) Late Cretaceous–Recent[1] PreЄ Є O S D C P T J K Pg N
European squid (Loligo vulgaris)
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Superorder:	Decapodiformes
Order:	Teuthida A. Naef, 1916
Suborders
†Plesioteuthididae (incertae sedis) Myopsina Oegopsina

Squid are 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 arranged in pairs and two, usually longer, tentacles. Squid are strong swimmers and certain species can 'fly' for short distances out of the water.^[2]

Modification from ancestral forms[link]

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

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

Anatomy[link]

Composite diagram illustrating basic squid features (ventral aspect)

The main body mass is enclosed in the mantle, which has a swimming fin 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 chromatophores, which enable the squid to change color to suit its surroundings, making it practically invisible. The underside is also almost always lighter than the topside, 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 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, to suit the direction of travel.

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

Nervous system[link]

The giant axon, which may be up to 1 mm (0.04 inches) in diameter in some larger species, innervates the mantle and controls part of the jet propulsion system.

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

Reproductive system[link]

A dissected male specimen of Onykia ingens, showing a non-erect penis (the white tubular structure located below most of the other organs)

A specimen of the same species exhibiting elongation of the penis to 67 cm in length

In females the ink sac is 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 organs are associated with food manufacture and shells for the eggs. Females also have a large translucent ovary, situated towards the posterior of the visceral mass.

Males 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 spermatophores, which are placed inside the female's mantle during mating.

Shallow water species of the continental shelf and epipelagic/mesopelagic zones are characterised by the presence of hectocotyli, specially modified arms used to fertilise the female's eggs.^[3] Most deep sea squid lack hectocotyli and have longer penises; Ancistrocheiridae and Cranchiinae are exceptions.^[3] Giant squid of the genus Architeuthis are unusual in that they possess both a large penis and modified arm tips, although it is uncertain whether the latter are used for spermatophore transfer.^[3] Penis elongation has been observed in the deep water species Onykia ingens; when erect, the penis may be as long as the mantle, head and arms combined.^[3][4] 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 barnacles.^[3]

Digestive system[link]

Like all cephalopods, squid have complex digestive systems. The muscular stomach is found roughly in the midpoint of the visceral mass. From there, the bolus moves 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 such that the stomach and caecum often shrivel up during the later life stages. Finally, food goes to the liver (or digestive gland), found at the siphon end, for absorption. Solid waste is passed out of the rectum. Beside the rectum is the ink sac, which allows a squid to rapidly discharge black ink into the mantle cavity.

Cardiovascular system[link]

Squid have three hearts. Two branchial hearts feed the gills, each surrounding the larger systemic heart that pumps blood around the body. Squid blood contains the copper-rich protein hemocyanin for transporting oxygen. The faintly greenish hearts are surrounded by the renal sacs - the main excretory system. The kidneys 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 ventricle and two upper auricles.

Head[link]

The head end 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, one basal half of the left ventral tentacle is hectocotylised — and ends in a copulatory pad rather than suckers. It is used for sexual intercourse.

The mouth is equipped with a sharp horny beak mainly made of chitin^[5] and cross-linked proteins, 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.^[6] Captured whales often have indigestible squid beaks in their stomachs. The mouth contains the radula (the rough tongue common to all molluscs except bivalvia).

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

Squid appear to have limited hearing.^[7]

Size[link]

A frozen giant squid in Melbourne Aquarium

The majority are no more than 60 centimetres (24 in) long, although the giant squid may reach 13 metres (43 ft).^[8]

In 1978, sharp, curved claws on the suction cups of squid tentacles cut up the rubber coating on the hull of the USS Stein. The size suggested the largest squid known at the time.^[9]

In 2003, a large specimen of an abundant^[10] but poorly understood species, Mesonychoteuthis hamiltoni (the colossal squid), was discovered. This species may grow to 14 metres (46 ft) in length, making it the largest invertebrate.^[11] Squid have the largest eyes in the animal kingdom. Giant squid are 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 New Zealand fishing vessel caught a colossal squid weighing 495 kilograms (1,090 lb) and measuring around 10 metres (33 ft) off the coast of Antarctica.^[12] This specimen represents the largest cephalopod to ever be scientifically documented.

Classification[link]

Bathyteuthis abyssicola

Grimalditeuthis bonplandi

Histioteuthis reversa

Mastigoteuthis flammea

Onychoteuthis banksii

Pterygioteuthis giardi

Squid are members of the class Cephalopoda, subclass Coleoidea, order Teuthida, of which there are two major suborders, Myopsina and Oegopsina (including giant squids like 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 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 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 squid.

• CLASS 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 (incertae sedis)
        • Suborder Myopsina
          • Family Australiteuthidae
          • Family Loliginidae: inshore, calamari, and grass squid
        • Suborder Oegopsina
          • Family Ancistrocheiridae: Sharpear Enope Squid
          • Family Architeuthidae: giant squid
          • Family Bathyteuthidae
          • Family Batoteuthidae: Bush-club Squid
          • Family Brachioteuthidae
          • Family Chiroteuthidae
          • Family Chtenopterygidae: comb-finned squid
          • Family Cranchiidae: glass squid
          • Family Cycloteuthidae
          • Family Enoploteuthidae
          • Family Gonatidae: armhook squid
          • Family Histioteuthidae: jewel squid
          • Family Joubiniteuthidae: Joubin's Squid
          • Family Lepidoteuthidae: Grimaldi Scaled Squid
          • Family Lycoteuthidae
          • Family Magnapinnidae: bigfin squid
          • Family Mastigoteuthidae: whip-lash squid
          • Family Neoteuthidae
          • Family Octopoteuthidae
          • Family Ommastrephidae: flying squid
          • Family Onychoteuthidae: hooked squid
          • Family Pholidoteuthidae
          • Family Promachoteuthidae
          • Family Psychroteuthidae: Glacial Squid
          • Family Pyroteuthidae: fire squid
          • Family Thysanoteuthidae: rhomboid squid
          • Family Walvisteuthidae
          • Parateuthis tunicata (incertae sedis)

Commercial fishing[link]

According to the FAO, the cephalopod catch for 2002 was 3,173,272 tonnes (6.995867×10⁹ lb). Of this, 2,189,206 tonnes, or 75.8 percent, was squid.^[13] The following table lists the squid species fishery catches which exceeded 10,000 tonnes (22,000,000 lb) in 2002.

As food[link]

Fried calamari: breaded, deep-fried squid

Many species are popular as food in cuisines as diverse as Chinese, Greek, Turkish, Japanese, Portuguese, Italian, Spanish, Korean, Vietnamese, and Filipino.

In English-speaking countries, squid as food is often marketed using the Italian word calamari. Squid are found abundantly in certain areas, and provide large catches for 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 that are not eaten are the beak and gladius (pen). Squid is a good food source for zinc, manganese and high in the recommended daily intake of copper,^[15] selenium, vitamin B12, and riboflavin.^[16]

See also[link]

• Paralarva

	Book: Cephalopoda
Wikipedia books are collections of articles that can be downloaded or ordered in print.

References[link]

External links[link]

Wikimedia Commons has media related to: Squid

Wikibooks Cookbook has a recipe/module on Squid

• CephBase: Teuthida
• Colossal Squid at the Museum of New Zealand Te Papa Tongarewa
• Market squid mating, laying eggs (video)
• Scientific American - Giant Squid
• The Cephalopod Page
• The Octopus News Magazine Online

v t e Principal commercial fishery species groups Wild Large pelagic fish Mackerel Salmon Shark Swordfish Tuna albacore bigeye Atlantic bluefin Pacific bluefin southern bluefin skipjack yellowfin Forage fish Anchovy Capelin Herring Ilish Menhaden Sardines Shad Demersal fish Catfish Cod Atlantic Pacific Flatfish flounder halibut plaice sole turbot Haddock Mullet Orange roughy Pollock Smelt-whitings Toothfish Freshwater fish Carp Sturgeon Tilapia Trout Other wild fish Eel Whitebait more... Crustaceans Crab Krill Lobster Shrimp and prawn more... Molluscs Abalone Mussels Octopus Oysters Scallops Squid more... Echinoderms Sea cucumbers Sea urchin more... Farmed Carp bighead common crucian grass silver Catfish Freshwater prawns Mussels Oysters Salmon Atlantic salmon trout coho chinook Scallops Seaweed Shrimp Tilapia Commercial fishing World fish production Fishing topics Fisheries glossary

v t e Edible mollusks Bivalves Clams Atlantic jackknife Atlantic surf Geoduck Grooved carpet shell Hard clam Horse Mactra stultorum Blunt gaper Ocean quahog Pacific razor Pecten jacobaeus Venus California butterclam Senilia senilis Smooth clam Soft-shell Triangle shell Tuatua Japanese littleneck Razor clam Pod razor Ensis (razor genus) Paphies Cockles Common Blood Goolwa New Zealand Mussels Blue Mediterranean New Zealand green-lipped California Brown Asian/Philippine green Date Mytilidae (mussel family) Oysters Auckland Eastern Olympia Southern mud Colchester native Pacific Portuguese Windowpane Rock Sydney rock Ostra chilena/Bluff Gillardeau oysters Crassostrea ("true oyster" genus) Scallops Atlantic bay Great/King New Zealand Peruvian calico Yesso Gastropods Abalone White Red Black Green Pink Blacklip Green ormer Pāua (group of 3 species) Chilean Conches Queen Dog Limpets Black foot opihi/Haiwaiian China Common European Rayed Mediterranean Ribbed Mediterranean Rustic Turtle/Talc Yellow foot opihi Periwinkles Common Banded Littorina sitkana Whelks Common Knobbed Lightning Channeled Other snails Sea Mud-flat Korean mud Chorus giganteus Land Helix aspersa Helix lucorum Helix pomatia Freshwater Nerites Inkfish Cuttlefish Spineless Bottletail Octopus Common Atlantic White-spotted Big Blue Pacific Giant Southern Red Amphioctopus fangsiao Squid New Zealand Arrow Japanese Flying Humboldt Neon flying Chitons Chiton magnificus Acanthopleura granulata Related topics: Oyster farming Land snail farming

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Dr. Widder at 33' depth in the Johnson Sea Link submersible

Edith Widder (born 1951) is an American oceanographer, marine biologist, and the Co-founder, CEO and Senior Scientist at the Ocean Research & Conservation Association.^[1][2][3]

She graduated from Tufts University magna cum laude with a B.S. in Biology, from University of California, Santa Barbara with an M.S. in Biochemistry, and from University of California, Santa Barbara with a PhD in Neurobiology, in 1982.^[4] She was a senior scientist and director of the Bioluminescence Department at the Harbor Branch Oceanographic Institution from 1989 to 2005.^[5] Certified as a Scientific Research Pilot for Atmospheric Diving Systems in 1984, she holds certifications that qualify her to dive the deep diving suit WASP^[2] as well as the single-person untethered submersibles DEEP ROVER and DEEP WORKER^[6] and she has made over 250 dives in the JOHNSON SEA LINK submersibles.^[7] Her research involving submersibles has been featured in BBC, PBS, Discovery Channel and National Geographic television productions.^[8][9][10]

A specialist in bioluminescence she has been a leader in helping to design and invent new instrumentation and techniques that enable scientists to see the ocean in new ways. These include HIDEX, a bathyphotometer which is the U.S. Navy standard for measuring bioluminescence in the ocean,^[11] and a remotely operated camera system, known as Eye in the Sea (EITS), an unobtrusive deep-sea observatory.^[12][13][14]

In 2005, Widder co- founded the Ocean Research & Conservation Association (ORCA), a non-profit organization dedicated to the protection of marine ecosystems and the species they sustain through development of innovative technologies and science-based conservation action. While translating complex scientific issues into engineerable solutions, Widder is fostering greater understanding of ocean life as a means to better, more informed ocean stewardship. In September 2006 she was awarded a prestigious MacArthur Fellowship from the John D. and Catherine T. MacArthur Foundation^[15] and in 2010 she participated in the TED Mission Blue Voyage in the Galapagos.^[16]

Awards[link]

• 2006 MacArthur Fellows Program

Works[link]

• Widder, E. A.; Latz, M. I.; Herring, P. J.; Case, J. F. (1984). "Far Red Bioluminescence from Two Deep-Sea Fishes". Science 225 (4661): 512–514. DOI:10.1126/science.225.4661.512. PMID 17750854.  edit
• Widder, E. A.; Bernstein, S. A.; Bracher, D. F.; Case, J. F.; Reisenbichler, K. R.; Torres, J. J.; Robison, B. H. (1989). "Bioluminescence in the Monterey Submarine Canyon: Image analysis of video recordings from a midwater submersible". Marine Biology 100 (4): 541–551. DOI:10.1007/BF00394831.  edit
• Widder, E. A. (2009). "Mixed light imaging system for recording bioluminescence behaviours". Journal of the Marine Biological Association of the United Kingdom 72: 131. DOI:10.1017/S0025315400048839.  edit
• Widder, E. A.; Greene, C. H.; Youngbluth, M. J. (1992). "Bioluminescence of sound-scattering layers in the Gulf of Maine". Journal of Plankton Research 14 (11): 1607–1624. DOI:10.1093/plankt/14.11.1607.  edit
• Widder, E.; Case, J.; Bernstein, S.; MacIntyre, S.; Lowenstine, M.; Bowlby, M.; Cook, D. (1993). "A new large volume bioluminescence bathyphotometer with defined turbulence excitation". Deep Sea Research Part I: Oceanographic Research Papers 40 (3): 607–627. DOI:10.1016/0967-0637(93)90148-V.  edit
• Widder, E.A. (1997) Bioluminescence – Shedding some light on plankton distribution patterns. Sea Technology March 1997:33–39.
• Widder, E. A. (1998). Environmental Biology of Fishes 53 (3): 267–273. DOI:10.1023/A:1007498915860.  edit
• Widder, E.A. (1999) Bioluminescence. In: “Adaptive Mechanisms in the Ecology of Vision.” Edited by: S.N. Archer, M.B.A. Djamgoz, E. Loew, J.C. Partridge & S. Vallerga. Kluwer Academic Publishers, Dordrecht, the Netherlands. pp 555–581.
• Johnsen, S., E.J. Balser and E.A. Widder. (1999) Modified suckers as light organs in a deep-sea octopod. Nature 398:113–114.
• Widder, E. A.; Johnsen, S.; Bernstein, S. A.; Case, J. F.; Neilson, D. J. (1999). "Thin layers of bioluminescent copepods found at density discontinuities in the water column". Marine Biology 134 (3): 429–437. DOI:10.1007/s002270050559.  edit
• Johnsen, S. and E.A. Widder. (1999) The physical basis of transparency in biological tissue: Ultrastructure and the minimization of light scattering. J. Theor. Biol. 199: 181–198
• Widder, E.A and S. Johnsen (2000) 3D spatial point patterns of bioluminescent plankton: A map of the “minefield” J. Plank. Res. 22(3): 409–420.
• Widder, E.A. (2000) Bioluminescence in octopods. Yearbook of Science and Technology. McGraw-Hill 2001: 52–55.
• Herring, P.J. and E.A. Widder (2001) Bioluminescence in plankton and nekton. In; Steele, J.H., Thorpe, S.A. and Turekian, K.K. editors, Encyclopedia of Ocean Science, Vol. 1, 308–317. Academic Press, San Diego.
• Widder, E. A.; Frank, T. M. (2001). "The speed of an isolume: A shrimp's eye view". Marine Biology 138 (4): 669–677. DOI:10.1007/s002270000504.  edit
• Widder, E.A. (2001) Bioluminescence. Bioscience Explained http://www.bioscience-explained.org/EN1.1/features.html Invited review.
• Widder, E. (2002). "Bioluminescence and the Pelagic Visual Environment". Marine and Freshwater Behaviour and Physiology 35: 1–26. DOI:10.1080/10236240290025581.  edit
• Widder, E. A. (2002). SPLAT CAM: Mapping plankton distributions with bioluminescent road-kill. pp. 1711–1715. DOI:10.1109/OCEANS.2002.1191891.  edit
• Widder, Edith (2002). The Bioluminescence Coloring Book. Harbor Branch Oceanographic Institution. ISBN 978-0-9659686-6-9. 
• Widder, E.A., C.L. Frey and L.J. Borne (2003) HIDEX Generation II: A New and Improved Instrument for Measuring Marine Bioluminescence. Marine Technology Society of the IEEE, Oceans 4:2214–2221
• Widder, E.A., C.L. Frey and J.R. Bowers (2005) Improved bioluminescence measurement instrument. Sea Technology 46(2): 10–16
• Widder, E.; Robison, B.; Reisenbichler, K.; Haddock, S. (2005). "Using red light for in situ observations of deep-sea fishes". Deep Sea Research Part I: Oceanographic Research Papers 52 (11): 2077–2085. DOI:10.1016/j.dsr.2005.06.007.  edit
• Widder, E.A. (2006) A look back at quantifying oceanic bioluminescence: Seeing the light, flashes of insight and other bad puns. Mar Tech Soc J. 40(2):136–137.
• Widder, E.A. (2007) Sly eye for the shy guy: Peering into the depths with new sensors Oceanography. 20(4): 46–51 (invited review)
• Widder, E. A. (2010). "Bioluminescence in the Ocean: Origins of Biological, Chemical, and Ecological Diversity". Science 328 (5979): 704–708. DOI:10.1126/science.1174269. PMID 20448176.  edit

Further reading[link]

• Collard, Sneed B. (2006). In the Deep Sea. New York: Marshall Cavendish Benchmark. ISBN 978-0-7614-1952-5. 

References[link]

External links[link]

• "Profile: Edith Widder", Science Now
• "Q&A: Edith Widder, MacArthur Fellow", Gulf of Maine Times, Lisa Capone, 2007
• Erik Olsen, "Illuminating the Perils of Pollution, Nature’s Way", New York Times, Dec. 19, 2011.

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