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Teuthida

(Order)

Overview

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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 and two tentacles arranged in pairs. (The only known exception is the bigfin squid group, which have ten very long, thin arms of equal length.)

Modification From Ancestral Forms

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Squid have differentiated from their ancestral molluscs 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 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 which supports the squid's mantle and serves as a site for muscle attachment. It is made of a chitin-like substance.

Anatomy

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European Squid (Loligo vulgaris)

The main body mass of the squid 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 ambulation in most species.

The skin of the squid is covered in chromatophores, which enable the squid to change color to suit its surroundings, making it effectively invisible. The underside of the squid is also almost always lighter in color 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 of the squid, which is covered by a thin, membranous epidermis. Under this are all the major internal organs of the squid.

Nervous System

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

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

Reproductive System

Egg cases laid by the female squid

In female squid, 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 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 spermatophores, 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

Ventral view of the viscera of Chtenopteryx sicula

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 ventricle and two upper auricles.

Head

The head end of the squid bears 8 arms and 2 tentacles (species in the bigfin squid group have 10 identical arms), 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 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[2] 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.[3] 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 bivalvia and 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 camera or telescope, rather than changing shape as the lens in the human eye does.

Size

Giant squid in Melbourne Aquarium
See also: Giant squid, Colossal Squid, and Cephalopod size

The majority of squid are no more than 60 centimetres (24 in) long, although the giant squid may reach 13 metres (43 ft) in length.[4]

In 1978, the "NOFOUL" rubber coating of the AN/SQS-26 SONAR dome 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.[5]

In 2003, a large specimen of an abundant[6] 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.[7] 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.[8]

Classification

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Caribbean Reef Squid, Bonaire.

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

Commercial Fishing

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According to the FAO, the total 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.[9] The following table lists the squid species fishery catches which exceeded 10,000 tonnes in 2002.

As Food

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Main article: Squid (food)
Fried calamari: breaded, deep-fried squid

Many species of squid are popular as food in cuisines as diverse as Greek, Japanese, Italian, Spanish and Korean.

In English-speaking countries, squid as food is often known by the Italia n word calamari.

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).

Photos

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Taxonomy

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The Order Teuthida is further organized into finer groupings including:

Families

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Ancistrocheiridae

The Sharpear Enope Squid (Ancistrocheirus lesueurii) is the only species in the genus Ancistrocheirus and family Ancistrocheiridae. With a mantle length of 25 , this moderately sized squid may be found throughout the tropical and subtropical oceans. They tend to be found at mesopelagic depths (200-1000 metres down). [more]

Architeuthidae

The giant squid (: Architeuthis) is a deep-ocean dwelling squid in the family Architeuthidae, represented by as many as eight species. Giant squid can grow to a tremendous size: recent estimates put the maximum size at 13 metres (43 ft) for females and 10 metres (33 ft) for males from caudal fin to the tip of the two long tentacles (second only to the colossal squid at an estimated 14 metres (46 ft), one of the largest living organisms). The mantle is about 2 metres (6.6 ft) long (more for females, less for males), and the length of the squid excluding its tentacles is about 5 metres (16 ft). There have been claims reported of specimens of up to 20 metres (66 ft), but no animals of such size have been scientifically documented. [more]

Bathyteuthidae

Bathyteuthis is the singular of squid in the family Bathyteuthidae, encompassing three species. None obtain a mantle length greater than 80 mm. [more]

Batoteuthidae

Bush-club Squid (Batoteuthis skolops) is the single rare in genus Batoteuthis, which is the only genus in family Batoteuthidae. The squid is found in Antarctic waters, and reaches a mantle length of at least 350 mm. Some features of this creature are a small head, a long tail and a very peculiar tentacle with six series of suckers on the club. [more]

Brachioteuthidae

Brachioteuthidae is a of squid. It contains two genera and around six species. [more]

Chiroteuthidae

Chiroteuthids are deep-sea of the family Chiroteuthidae. They are generally small to medium in size, rather soft and gelatinous, and slow moving. They are found in most temperate and tropical oceans, but are known primarily from the North Atlantic, North Pacific, and Indo-Pacific. The family is represented by approximately twelve species and four subspecies in four genera, two of which are monotypic. They are sometimes known collectively as whip-lash squid: However, this common name is also applied to the Mastigoteuthidae, which is itself sometimes treated as a subfamily (Mastigoteuthinae) of Chiroteuthidae. [more]

Chtenopterygidae

Chtenopteryx is a genus of small, muscular, midwater in the monotypic family Chtenopterygidae. Four species are presently recognized in the genus, but more are believed to exist. [more]

Cranchiidae

The family Cranchiidae comprises the approximately 60 species of glass squid, also known as cranchiid or cranch squid. Cranchiid squid occur in surface and midwater depths of open oceans around the world. They range in length from 10 centimetres (3.9 in) to over 3 metres (9.8 ft), in the case of the Colossal Squid. The common name, glass squid, derives from the transparent nature of most species. Cranchiid squid spend much of their lives in partially sunlit shallow waters where their transparency provides camouflage. They are characterised by a swollen body and short arms, which bear two rows of suckers or hooks. The third arm pair is often enlarged. Many species are bioluminescent organisms and possess light organs on the undersides of their eyes, used to cancel their shadow. Eye morphology varies widely, ranging from large and circular to telescopic and stalked. A large fluid-filled chamber containing ammonia solution is used to aid buoyancy. Often the only organ that is visible through the transparent tissues is a cigar-shaped digestive gland, which is the cephalopod equivalent of a mammalian liver. This is usually held in a vertical position to reduce its silhouette and a light organ is sometimes present on the lower tip to further minimise its appearance in the water. [more]

Ctenopterygidae

[more]

Cycloteuthidae

Cycloteuthidae is a in the order Teuthida, comprising two genera. While physically dissimilar, molecular evidence supports the relatedness of the genera. The family is found primarily in mesopelagic tropical to subtropical waters. Cycloteuthidae is characterised by a triangular funnel-locking apparatus. [more]

Enoploteuthidae

Enoploteuthidea is a of squid comprising approximately 40 species in 4 genera. Most species have a mantle length ranging from 3-13 cm. Hooks are present on all arms and tentacles. The family is best known for the large array of photophores throughout the body. [more]

Gonatidae

The Gonatidae, also known as armhook squid, are a of moderately-sized squid. The family contains approximately 19 species in three genera, widely distributed and plentiful in cold boreal waters of the Pacific Ocean. At least one species is known from Antarctic waters, and two from the North Atlantic. [more]

Histioteuthidae

Histioteuthis is a genus of and the only member of the Histioteuthidae family. It goes by the English name cock-eyed squid, because in all species the right eye is normal-sized, round, blue and sunken; whereas the left eye is at least twice the diameter of the right eye, tubular, yellow-green, faces upward, and bulges out of the head. They live at depths of around 2500 ft and can change color slightly.[citation needed] [more]

Joubiniteuthidae

Joubin's Squid (Joubiniteuthis portieri) is a rare, small found in both the Atlantic Ocean, Pacific Ocean and in rare cases, the Indian Ocean. The species is named after Louis Joubin, a French zoologist. It is known to reach a mantle length of 9 cm. [more]

Lepidoteuthidae

Grimaldi Scaled Squid is a named after the Grimaldi family, reigning house of Monaco. Prince Albert I of Monaco was an amateur teuthologist who pioneered the study of deep sea squids by collecting the 'precious regurgitations' of Sperm Whales. Grimaldi Scaled Squid was first collected from the stomach contents of a whale. [more]

Loliginidae

Loliginidae is an aquatic of the order Teuthida (squid). [more]

Lycoteuthidae

Lycoteuthidae is a family of comprising four known genera in two subfamilies. They are characterised by a lack of hooks and by photophores present on the viscera, eyeballs and tentacles. [more]

Magnapinnidae

The bigfin squids are a group of rarely seen with a very distinctive morphology. They are placed in the genus Magnapinna and family Magnapinnidae. The family is known only from larval, paralarval, and juvenile specimens, but some authorities believe the adult creature has been seen: Several videos have been taken of animals nicknamed the "long-arm squid", which appear to have a similar morphology. Since none of the adult specimens have ever been captured or sampled, it remains uncertain if they are the same genus, or only distant relatives. [more]

Mastigoteuthidae

The Mastigoteuthidae, also known as whip-lash squid, are a family of small deep-sea . Approximately 20 known species in two genera are represented, with members found in both the mesopelagic and bathypelagic zone of most oceans. They are sometimes treated as a subfamily (Mastigoteuthinae) of the Chiroteuthidae, which are also called whip-lash squid on occasion. [more]

Neoteuthidae

Neoteuthidae is a of squid comprising four monotypic genera. [more]

Octopoteuthidae

Octopoteuthidae is a of squid comprising two genera. The family is characterised by tentacles which cease to grow after the paralarval stage; and the use of a penis, instead of a hectocotylus. [more]

Ommastrephidae

Ommastrephidae is a of squid. It contains 3 subfamilies, 11 genera, and over 20 species. [more]

Onychoteuthidae

The Onychoteuthidae (Hooked squid) currently comprises approximately 20-25 species (several known from only single life stages and thus unconfirmed), in 6 or 7 genera. They range in mature mantle length from 7 cm to a suggested length of 2 m for the largest member, the Robust Clubhook Squid (Moroteuthis robusta). The family is characterised by the presence of hooks only on the tentacular clubs, simple straight mantle-funnel-locking apparatus, and a 'step' inside the jaw angle of the lower beak. With the exception of the Arctic Ocean, the family is found worldwide. [more]

Pholidoteuthidae

Pholidoteuthis is a of squid in the monotypic family Pholidoteuthidae, comprising at least two species. The defunct genus Tetronychoteuthis was previously incorporated into Pholidoteuthidae based upon a singular taxon known as Tetronychoteuthis massyae. Following the discovery of Pholidoteuthis boschmai in 1950, T. massaye was placed into Pholidoteuthis, with Tetronoychoteuthis considered a nomen dubium. It must be noted that P. boschmai is now considered a junior synonym of P. massyae. [more]

Promachoteuthidae

Promachoteuthis is a of small, weakly muscled squid found at bathypelagic depths. Three species have been formally described, while another two await description. [more]

Psychroteuthidae

The Glacial Squid (Psychroteuthis glacialis) is the only known species in the genus Psychroteuthis, in the family Psychroteuthidae. While only one species has been confirmed, it is possible that two undescribed species also exist. The species occurs in coastal waters near Antarctica and South America. It grows to a mantle length of 44 cm. [more]

Pyroteuthidae

Fire squid are species belonging to the family Pyroteuthidae. The family comprises two . Species are diurnally mesopelagic, however migrate into surface waters during the night. The family is characterised by the tentacles, which have a permanent constriction and bend near the base; and photophores occurring on the tentacles, eyeballs and viscera. Members reach mantle lengths of 23-50 mm. Paralavae of the family are common around the Hawaiian Islands, with up to 17% of collected specimens in the area belonging to Pyroteuthidae. [more]

Thysanoteuthidae

Thysanoteuthis is a of large squid comprising one well known species, the Diamond Squid, and two dubious taxa. [more]

Uncertain Taxonomic Position

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Walvisteuthidae

Walvisteuthis is a of squid consisting of a single species, Walvisteuthis virilis. It is found in the southern Atlantic Ocean. Walvis (the Dutch word for whale) refers to the Walvis Ridge in the South Atlantic; virilis (Latin for male) was chosen because only one, male, specimen was ever caught. [more]

More info about the Family Walvisteuthidae may be found here.

References

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  1. ^ Tanabe, K.; Hikida, Y.; Iba, Y. (2006), "Two Coleoid Jaws from the Upper Cretaceous of Hokkaido, Japan", Journal of Paleontology 80 (1): 138–145, doi:10.1666/0022-3360(2006)080[0138:TCJFTU]2.0.CO;2 
  2. ^ Clarke, M.R. (1986). A Handbook for the Identification of Cephalopod Beaks. Oxford: Clarendon Press. ISBN 0-19-857603-X. 
  3. ^ Miserez, A; Li, Y; Waite, H; Zok, F (2007). "Jumbo squid beaks: Inspiration for design of robust organic composites". Acta Biomaterialia 3: 139–149. doi:10.1016/j.actbio.2006.09.004. 
  4. ^ O'Shea, S. 2003. "Giant Squid and Colossal Squid Fact Sheet". The Octopus News Magazine Online.
  5. ^ Johnson, C. Scott "Sea Creatures and the Problem of Equipment Damage" United States Naval Institute Proceedings August 1978 pp.106-107
  6. ^ Xavier, J.C., P.G. Rodhouse, P.N. Trathan & A.G. Wood 1999. A Geo graphical Information System (GIS) Atlas of cephalopod distribution in the Southern Ocean.PDF Antarctic Science 11:61-62. online version
  7. ^ Anderton, H.J. 2007. Amazing specimen of world's largest squid in NZ. New Zealand Government website.
  8. ^ Microwave plan for colossal squid. BBC News March 22, 2007.
  9. ^ a b Rodhouse, Paul G (2005) Review of the state of world marine fishery resources: World squid resources. FAO: Fisheries technical paper, No 447. ISBN 95-5-105267-0
  10. ^ a b nei: not elsewhere included

Sources

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Last Revised: September 22, 2009
2009/09/22 08:24:12