Thysanoteuthis rhombus

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Diamond squid
Thysanoteuthis rhombus.jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Oegopsida
Family: Thysanoteuthidae
Genus: Thysanoteuthis
Species:
T. rhombus
Binomial name
Thysanoteuthis rhombus
Troschel, 1857 [2]
Synonyms
  • Cirrobrachium danae Joubin, 1933
  • Cirrobrachium filiferum Hoyle, 1904
  • Sepioteuthis major Gray, 1828
  • Thysanoteuthis elegansTroschel, 1857

Thysanoteuthis rhombus, also known as the diamond squid,diamondback squid, or rhomboid squid, is a large species of squid from the family Thysanoteuthidae which is found worldwide, throughout tropical and subtropical waters. T. rhombus is given its name for the appearance of the fins that run the length of the mantle. They are a fast growing species with a lifespan of approximately 1 year. The diamond squid is the only cephalopod species known to be monogamous. T. rhombus often preys on fish and other small cephalopods at varying water depths. This species is commercially fished in Japan, specifically in the Sea of Japan and Okinawa. [3]

Contents

Description

Thysanoteuthis rhombus are distinguishable by the presence of arms with two series of suckers, whereas the tentacular clubs have four. It lacks photophores. T. rhombus is named for its fins, which run in equal length along the mantle, giving the appearance of a rhombus. The species is able to grow up to 100 cm (3.3 ft) in mantle length [4] and a maximum weight of 30 kg, [5] although it averages around 20 kg. [6] T. rhombus is not an active swimmer and propels itself slowly using its triangular fins, although the species is able to make powerful contractions of its mantle to escape predation. [7]

T. rhombus in the Gulf of Naples. I Cefalopodi viventi nel Golfo di Napoli (sistematica) (Tav. 9) (6105707033).jpg
T. rhombus in the Gulf of Naples.

The lifespan of T. rhombus is 1 year. Males mature at a mantle length between 400 to 550mm (170 to 200 days of age) while females mature at a mantle length between 550 to 650mm (230 to 250 days). [8]

Behavior

The species is one of the only cephalopods observed exhibiting pair-like mating relationships. If one member of a male-female mating pair is caught by squid fishermen, the other will likely remain in the area until it is also caught. [9] The species feeds during the daytime at deep water levels and during the night at shallow water levels. [7] T. rhombus are often found in pairs [8] , but groups up to 20 have been recorded [10] .

T. rhombus typically inhabits open ocean waters of the subtropical and tropical locations with temperatures of >20°C. [9] The diamond squid was found to be largely inactive or even die at depths of 0–100m due to sudden drops in temperatures below 15°C. [11]

Diet

In subsurface water levels, T. rhombus juveniles were found to feed on crustaceans, small cephalopods and fishes. [12] As adults, the stomach contents of the Diamond squid were found to consist mostly of nonactive fishes at water depths of 400 to 650m. [13]

Predation

The predators that feed on T. rhombus include various species of ommastrephid squids, dolphin fish, lancet fish, tuna, swordfish, Gempylus serpens , and sharks. Other predators include mammals such as dolphins, rough-toothed dolphin, false killer whale and sperm whale. [14]

Reproduction

Thysanoteuthis rhombus egg mass (diameter ca. 1m) in the waters between Tenerife and La Gomera. Thysanoteuthis rhombus egg mass - ZooKeys-222-069-g002-10.jpeg
Thysanoteuthis rhombus egg mass (diameter ca. 1m) in the waters between Tenerife and La Gomera.

The pairing of males and females occurs at an immature stage where mantle length is less than 100mm and pairs remain monogamous. [15] Mating occurs in a head-to-head position, in which the male uses its hectocotylus to attach to the female's buccal membrane to transfer its spermatophores. Spawning is year round in tropical waters and lasts for 2–3 months, but in temperate regions spawning is more restricted to summer or early autumn periods and warmer currents. T. rhombus is known to be an intermittent spawner and is known to have multiple spawning in succession. [16] Females will produce secretions of gel-like substance from nidamental glands, similar to the Japanese flying squid, during spawning that will enter the water and swell. This swollen secretion will then be molded by the female into a cylinder. Female's oviductal glands will then begin to form two mucous threads, each with one row of eggs, which will fuse into a single cord containing a double row of eggs in the mantle cavity. The fused cord exits through into the water through the funnel where the eggs are met and fertilized with spermatozoa from seminal receptacles that were attached to the female's buccal membrane. The fertilized egg cord is then wound onto the cylinder. A female can produce 8 to 12 masses if properly utilizing its vitelline oocytes. [7]

Commercial value

T. rhombus is targeted by growing fisheries in near southern and central Japan due to its firm and flavorful flesh. The main fishing grounds are in the Sea of Japan, Okinawa Prefecture, and Kagoshima Prefecture. Majority, about 90%, of captures are located in the Sea of Japan and Okinawa. The Sea of Japan fishery runs from July to February, while the fishery in Okinawa runs primarily between November to April. To capture the diamond squid in the Sea of Japan, inshore trap nets and free-floating angling gear called "taru-nagashi" are used. In Okinawa, free-floating angling gear called "Hata-nagashi" is used for capture. [3]

"Taru-nagashi" is gear that consists of a vertical weighted long line with two or three artificial lures and with two or three rows of stainless steel hooks. At the other end of the line, an orange fluorescent buoy lays on its side on the surface until a squid hooks onto the line, which causes buoy stands up to alert the fisherman. The caught squid are pulled up by hand or by using a winch, so it is primarily used during the day. "Hata-nagashi" is gear that was adapted for the oceanographic conditions of Okinawa Prefecture. It has several artificial lures attached to a longer main line than those used in the Sea of Japan. The line is attached to several buoys and a flag at the surface. This gear lead to the increase of catches of T. rhombus. [17]

See also

Related Research Articles

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Humboldt squid Species of cephalopod

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Firefly squid Species of cephalopod also known as the sparkling enope squid

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European squid Species of cephalopods

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Japanese flying squid species of mollusc

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Neon flying squid species of mollusc

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Bigfin reef squid species of mollusc

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<i>Illex coindetii</i> species of mollusc

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<i>Illex illecebrosus</i> Species of cephalopod known as the northern shortfin squid

Illex illecebrosus, commonly known as the northern shortfin squid, is a species of neritic squids in the family Ommastrephidae. They are found in the northwest Atlantic Ocean, from off the coast of eastern North America to Greenland, Iceland, and west of Ireland and the United Kingdom. They are a highly migratory and short-lived species, with lifespans of less than a year. They are commercially important and are fished extensively, mostly for the Canadian and Japanese markets. Northern shortfin squid is a migratory species of squid with a distribution ranging from Florida Straits to Newfoundland in the Northwest Atlantic Ocean. The species is native to Canada, Greenland, Iceland and United States. The species has an average lifespan between 1–1.5 years in which most live less than a year. The location of the fishery of the squid is mainly in Mid-Atlantic Bight from between summer and fall.

<i>Sthenoteuthis pteropus</i> species of mollusc

Sthenoteuthis pteropus, also known as the orangeback flying squid or orangeback squid, is a species of cephalopod in the family Ommastrephidae. It is native to tropical parts of the Atlantic Ocean where it is found to depths of about 200 m (656 ft).

<i>Sepioteuthis australis</i> species of mollusc

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<i>Sthenoteuthis oualaniensis</i> species of mollusc

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References

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