Gonatidae

Taxobox
name = Gonatidae

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image_width = 200px
image_caption = Magister Armhook Squid
regnum = Animalia
phylum = Mollusca
classis = Cephalopoda
subclassis = Coleoidea
ordo = Teuthida
subordo = Oegopsina
familia = Gonatidae
familia_authority = Hoyle, 1886
subdivision_ranks = Genera
subdivision = "Berryteuthis"
"Eogonatus"
"Gonatopsis"
"Gonatus"The Gonatidae, also known as armhook squid, are a family 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.

Physical description

Morphologically, armhook squid are fairly uniform: all species are characterised by the suckers of their arms, which are arranged in four rows ("series") rather than the typical count of two. In most species the arm's two mesial rows of suckers have been modified into hooks and the tentacular clubs—which are covered with many irregular rows of tiny suckers—may possess an enlarged central hook, with or without several smaller hooks. In the Magister Armhook Squid ("Berryteuthis magister"), it is only the females who possess hooks. Species of the genus "Gonatus" differ from the rest of the family (and from most squid) by their lack of tentacles as adults.

Only one species, the Fiery Armhook Squid ("Gonatus (Gonatus) pyros"), possesses photophores; these are located on the ventral periphery of the eyes.

Gonatids typically have muscular, cylindrical bodies with very soft, reddish to purplish brown skin. The arms are thick and capable; the fins vary in shape and size, from and about 50 percent of the mantle length, to reniform and about 30 percent of the mantle length. Of moderate size, these squid range in size from 11 centimetres to 40 centimetres—most species are 25 centimetres or less. Females are somewhat larger than males.

Life history

These squid are pelagic, associated with the continental shelf and may roam as deep as 4,500 metres or more, depending on the species. Their habits are poorly studied, but the squid are thought to undertake diel migration; by day the squid remain in the blackness of the depths in midwater. By night, they ascend to the upper layers of the water column to feed by starlight. One species however, "Gonatopsis (Gonatopsis) octopedatus", has curiously recurved arms, suggesting a benthic existence.

Little is known about the reproductive cycle of armhook squid. Most squid species whose reproduction has been obeserved have been seen to deposit eggs on the sea floor than leave the eggs to hatch on their own. Five female "Gonatus onyx" squids have been observed in Monterey Canyon dragging a membrane sack containing 2,000 to 3,000 developing eggs. [cite journal | first = BA | last = Seibel | coauthors = Robison BH, Haddock SH | year = 2005 | month = December 15 | title = Post-spawning egg care by a squid | journal = Nature | volume = 438 | issue = 7070 | pages = 929 | pmid = 16355206 | accessdate = 2006-09-26 | doi = 10.1038/438929a] It is uncertain if this behavior extends to other members of the Gonatidae family or if it is particular to this species.

Prey items include both benthic and pelagic species, including; smaller fish such as sculpins and juvenile pollock, crustaceans including euphausiids and amphipods, and other squid. Cannibalism is also known to occur among the Gonatidae.

Cetaceans are important predators of gonatids; Baird's Beaked Whale, the Short-finned Pilot Whale, Dall's Porpoise and Sperm Whales are all known to feed upon them. Other predators include large seabirds, Northern Fur Seals and Elephant Seals, large fish such as grenadiers, halibut and several species of salmon. In far southern waters, Weddell Seals and Southern Fur Seals as well as several species of albatross and penguin feed upon "Gonatus (Gonatus) antarcticus".

pecies

*Genus "Berryteuthis"
**Minimal Armhook Squid, "Berryteuthis anonychus"
**"Berryteuthis magister"
***Magister Armhook Squid, "Berryteuthis magister magister"
***"Berryteuthis magister nipponensis"
***"Berryteuthis magister shevtsovi"
*Genus "Eogonatus"
**"Eogonatus tinro"
*Genus "Gonatopsis"
**Boreopacific Armhook Squid, "Gonatopsis (Boreoteuthis) borealis"
**"Gonatopsis (Gonatopsis) japonica"
**Makko Armhook Squid, "Gonatopsis (Gonatopsis) makko"
**"Gonatopsis (Gonatopsis) octopedatus"
**"Gonatopsis (Gonatopsis) okutanii" *
*Genus "Gonatus"
**"Gonatus antarcticus"
**Berry Armhook Squid, "Gonatus berryi"
**California Armhook Squid, "Gonatus californiensis"
**Boreoatlantic Armhook Squid, "Gonatus fabricii"
**"Gonatus kamtschaticus"
**Madokai Armhook Squid, "Gonatus madokai"
**Clawed Armhook Squid or Black-eyed Squid, "Gonatus onyx"
**Oregon Armhook Squid, "Gonatus oregonensis"
**Fiery Armhook Squid, "Gonatus pyros"
**Atlantic Armhook Squid, "Gonatus steenstrupi"
**Brown Bear Armhook Squid, "Gonatus ursabrunae"

The species listed above with an asterisk (*) is questionable and needs further study to determine if it is a valid species or a synonym.

References

External links

* [http://tolweb.org/Gonatidae Tree of Life web project: Gonatidae]
* [http://www.tonmo.com/forums/forumdisplay.php?f=40 Gonatidae discussion forum at TONMO.com]
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