''Berryteuthis magister'', also known as the magister armhook squid, commander squid or schoolmaster gonate squid, is a medium-sized

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Gonatidae The Gonatidae, also known as armhook squid, are a family of moderately sized squid. The family contains about 19 species in three genera, widely distributed and plentiful in cold boreal waters of the Pacific Ocean. At least one species is known f ...

. It is found in cold, high latitude waters of the North Pacific where it is among the most numerous squid

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

recorded. There are three recognised

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

of ''B. magister''. The type locality of all three is

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

, although specimens have been recorded as far east as the

Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi language, Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a cha ...

Description

The cylindrical bodies of magister armhook squid are muscular with very soft reddish brown skin. Like all

gonatid The Gonatidae, also known as armhook squid, are a family of moderately sized squid. The family contains about 19 species in three genera, widely distributed and plentiful in cold boreal waters of the Pacific Ocean. At least one species is known ...

s, the suckers of their arms are arranged in four rows or ''series''. But unlike other gonatids it is in females only that the suckers are modified into hooks; these hooks are on the mesial rows of the dorsal arms only. The clubs at the end of both

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s are covered in 20 rows of suckers; these are smaller in ''B. magister nipponensis''. The wing-like fins at the rear of the body are rather large and may reach up to 50 percent of the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

length. The fins are also smaller in ''B. magister nipponensis''. ''B. magister magister'' is known to reach a mantle length of ; total body length may exceed . Both ''B. magister nipponensis'' and ''B. magister shevtsovi'' are somewhat smaller, with a maximum mantle length of . Females are slightly larger than males. Image:Berryteuthis magister2.jpg, Ventral view Image:Berryteuthis magister3.jpg, Oral view Image:berryteuthis magister hooks.jpg, Close-up of hooks Image:Berryteuthis magister4.jpg, Tentacular club Image:Berryteuthis magister5.jpg, Tentacular club

Habitat and behaviour

These squid are

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

, roaming as deep as 1,000 metres and are associated with the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

. Like other species in their family, Magister Armhook Squids are thought to undertake

diel Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24-h ...

migration; by day the squid remain in the blackness of the depths. By night, they ascend to the upper layers of the water column to feed by starlight. An internal balancing organ called a '' statocyst'' ensures graceful movement. Magister armhook squid prey upon both

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

and pelagic species;

sculpin A sculpin is a type of fish that belongs to the superfamily Cottoidea in the order Scorpaeniformes.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology suggest transitions in station-holding demand a ...

s, smaller

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

such as Sablefish and juvenile pollock,

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s including

euphausiid Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are consi ...

s and

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

s, and other squid.

Cannibalism Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, b ...

is also known to occur among the Magisters. Baird's beaked whale, the short-finned pilot whale, false killer whale, Dall's porpoise and

sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale famil ...

s are all known to feed upon magister armhook squid. Other predators include

seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...

northern fur seal The northern fur seal (''Callorhinus ursinus'') is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the ...

grenadier A grenadier ( , ; derived from the word '' grenade'') was originally a specialist soldier who threw hand grenades in battle. The distinct combat function of the grenadier was established in the mid-17th century, when grenadiers were recruited fr ...

halibut Halibut is the common name for three flatfish in the genera '' Hippoglossus'' and ''Reinhardtius'' from the family of right-eye flounders and, in some regions, and less commonly, other species of large flatfish. The word is derived from ''h ...

and several species of

salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

References

External links

(''Berryteuthis magister magister'') (''Berryteuthis magister nipponensis'') (''Berryteuthis magister shevtsovi'')
Tree of Life web project: ''Berryteuthis magister''Tree of Life web project: ''Berryteuthis magister nipponesis''Tree of Life web project: ''Berryteuthis magister shevtsovi''
{{Taxonbar, from=Q1957918 Squid Molluscs of the Pacific Ocean Molluscs described in 1913 Taxa named by Samuel Stillman Berry