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The Gonatidae, also known as armhook squid, are a family of moderately sized squid. The family contains about 19 species in three genus, widely distributed and plentiful in cold boreal waters of the Pacific Ocean. At least one species is known from Antarctica waters, and two from the North Atlantic. The genus Eogonatus was created for the species known as Eogonatus tinro because it did not have hooks on the tentacular club and it has 5 rows of teeth on the radula. Molecular studies in allozymes and mitochondrial DNA have indicated that this species nests within the genus Gonatus, although other authorities treat it as a synonym of Gonatopsis okutanii.
Only one species, the fiery armhook squid ( Gonatus pyros), possesses ; these are located on the ventral periphery of the cephalopod eye.
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% of the mantle length, to reniform and about 30% of the mantle length. Of moderate size, these squid range in size from 11 to 40 cm—most species are 25 cm or less. Females are somewhat larger than males.
Little is known about the reproductive cycle of armhook squid. Most squid species whose reproduction has been observed have been seen to deposit eggs on the sea floor, then 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. It is uncertain if this behavior extends to other members of the family Gonatidae or if it is particular to this species.
Prey items include both benthos and pelagic species, including smaller fish, such as and juvenile pollock, , including and , and other squid. Cannibalism is also known to occur among the Gonatidae.
are important predators of gonatids; Baird's beaked whale, the narwhal, the short-finned pilot whale, Dall's porpoise, and are all known to feed upon them. Other predators include large , northern fur seals, , and large fish, such as Rattail, halibut and several species of salmon. In far southern waters, and southern fur seals, as well as several species of albatross and penguin, feed upon Gonatus antarcticus.
The species listed above with an asterisk (*) is questionable and needs further study to determine if it is a valid species or a synonym.
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