Magister Armhook Squid
Encyclopedia
The Magister Armhook Squid (Berryteuthis magister), also known as the Commander Squid or Schoolmaster Gonate Squid, is a medium-sized squid
in the family
Gonatidae
. It is found in cold, high latitude waters of the North Pacific
where it is among the most numerous squid species
recorded.
There are three recognised subspecies
of B. magister. The type locality of all three is Japan
, although specimens have been recorded as far east as the Aleutian Islands.
s 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
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
length. The fins are also smaller in B. magister nipponensis.
B. magister magister is known to reach a mantle length of 25 centimetres; total body length may exceed 61 centimetres (2 feet). Both B. magister nipponensis and B. magister shevtsovi are somewhat smaller, with a maximum mantle length of 17-20 centimetres. Females are slightly larger than males.
, roaming as deep as 1,000 metres and are associated with the continental shelf
. Like other species in their family, Magister Armhook Squids are thought to undertake diel
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
and pelagic species; sculpin
s, smaller fish
such as Sablefish
and juvenile pollock
, crustacean
s including euphausiids and amphipods, and other squid. Cannibalism
is also known to occur among the Magisters.
Baird's Beaked Whale, the Short-finned Pilot Whale
, Dall's Porpoise
and Sperm Whale
s are all known to feed upon Magister Armhook Squids. Other predators include seabird
s, Northern Fur Seal
s, Grenadier
s, halibut
and several species of salmon
.
(Berryteuthis magister nipponensis)
(Berryteuthis magister shevtsovi)
Squid
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...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Gonatidae
Gonatidae
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...
. It is found in cold, high latitude waters of the North Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
where it is among the most numerous squid species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
recorded.
There are three recognised subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
of B. magister. The type locality of all three is Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, although specimens have been recorded as far east as the Aleutian Islands.
Physical description
The cylindrical bodies of Magister Armhook Squids are muscular with very soft reddish brown skin. Like all gonatids, the suckers of their armCephalopod arm
A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...
s 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
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
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
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
length. The fins are also smaller in B. magister nipponensis.
B. magister magister is known to reach a mantle length of 25 centimetres; total body length may exceed 61 centimetres (2 feet). Both B. magister nipponensis and B. magister shevtsovi are somewhat smaller, with a maximum mantle length of 17-20 centimetres. Females are slightly larger than males.
Habitat and behaviour
These squid are pelagicPelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
, roaming as deep as 1,000 metres and are associated with the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
. Like other species in their family, Magister Armhook Squids are thought to undertake diel
Diel
People with the surname Diel:* Charles Diel, former head men’s tennis coach at Louisiana State University* Paul Diel , French psychologistDiel may also refer to:* Diel vertical migration, common among deep-sea fish...
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
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...
ensures graceful movement.
Magister Armhook Squid prey upon both benthic
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
and pelagic species; sculpin
Sculpin
A Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
s, smaller fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate 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...
such as Sablefish
Sablefish
The sablefish, Anoplopoma fimbria, is one of two members of the fish family Anoplopomatidae and the only species in the Anoplopoma genus...
and juvenile pollock
Pollock
Pollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...
, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s including euphausiids and amphipods, and other squid. Cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
is also known to occur among the Magisters.
Baird's Beaked Whale, the Short-finned Pilot Whale
Short-finned Pilot Whale
The Short-finned Pilot Whale is one of the two species of cetacean in the genus Globicephala. It is part of the oceanic dolphin family , though its behaviour is closer to that of the larger whales....
, Dall's Porpoise
Dall's Porpoise
Dall's porpoise is a species of porpoise found on the North Pacific. It came to worldwide attention in the 1970s when it was disclosed for the first time to the public that salmon fishing trawls were killing a lot, thousands of Dall's porpoises and other cetaceans each year by accidentally...
and Sperm Whale
Sperm Whale
The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter...
s are all known to feed upon Magister Armhook Squids. Other predators include seabird
Seabird
Seabirds are birds that have 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 environmental problems and feeding niches have resulted in similar adaptations...
s, Northern Fur Seal
Northern Fur Seal
The Northern fur seal 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 and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...
s, Grenadier
Rattail
Grenadiers or rattails are generally large, brown to black gadiform marine fish of the family Macrouridae...
s, halibut
Halibut
Halibut is a flatfish, genus Hippoglossus, from the family of the right-eye flounders . Other flatfish are also called halibut. The name is derived from haly and butt , for its popularity on Catholic holy days...
and several species of salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
.
External links
(Berryteuthis magister magister)(Berryteuthis magister nipponensis)
(Berryteuthis magister shevtsovi)