The Colossal Squid (Mesonychoteuthis hamiltoni, from Greek mesos (middle), nychus (claw), and teuthis (squid)), sometimes called theAntarctic or Giant Cranch Squid, is believed to be the largest squid species in terms of mass. It is the only known member of the genusMesonychoteuthis. Though it is known from only a few specimens, current estimates put its maximum size at 12–14 metres (39–46 feet)long,[1] based on analysis of smaller and immature specimens, making it the largest known invertebrate.
Morphology
Unlike the giant squid, whose arms and tentacles only have suckers lined with small teeth, the Colossal Squid's limbs are also equipped with sharp hooks: some swiveling, others three-pointed.[2] Its body is wider and stouter, and therefore heavier, than that of the giant squid. Colossal Squids are believed to have a longer mantle than giant squids, although their tentacles are shorter.
The squid exhibits abyssal gigantism. The beak of Mesonychoteuthis hamiltoni is the largest known of any squid, exceeding that of Architeuthis(giant squid) in size and in robustness. The Colossal Squid also has the largest eyes documented in the animal kingdom.[3]
[edit]Distribution
The squid's known range extends thousands of miles northward from Antarctica to southern South America, southern South Africa, and the southern tip of New Zealand, making it primarily an inhabitant of the entire circumantarctic Southern Ocean.
[edit]Ecology and life history
While little is known about the life of this creature, it is believed to feed on prey such as chaetognatha, large fish like the Patagonian toothfishand other squid in the deep ocean using bioluminescence. The Colossal Squid is thought to have a slow metabolic rate, requiring only around 30 g of prey daily.[4] Estimates of its energetic demands suggest that it is a slow-moving ambush predator, using its large eyes primarily for predator detection rather than active hunting.[4][5]
Based on capture depths of a few specimens, as well as beaks found in sperm whale stomachs, the adult squid ranges at least to a depth of 2200 metres, while juveniles can go as deep as 1000 metres. It is believed to be sexually dimorphic, with mature females generally being much larger than mature males, as is common in many species of invertebrates.
The squid's method of reproduction has not been observed, although some data on their reproduction can be inferred from anatomy. Since males lack an organ called a hectocotylus (a tentacle used in other cephalopods to transfer a spermatophore to the female), they probably use a penis instead, which would be used to directly implant sperm into females.
Many sperm whales carry scars on their backs believed to be caused by the hooks of Colossal Squid. Colossal Squid are a major prey item for Antarctic sperm whales feeding in the Southern Ocean; 14% of the squid beaks found in the stomachs of these sperm whales are those of the Colossal Squid, which indicates that Colossal Squid make up 77% of the biomass consumed by these whales.[6] Many other animals also feed on this squid, including beaked whales (such as the bottlenose whales), pilot whales, southern elephant seals,Patagonian toothfish, sleeper sharks (Somniosus cf. microcephalus), and albatrosses (e.g., the Wandering and Sooty albatrosses). However, beaks from mature adults have only been recovered from those animals large enough to take such prey (i.e., sperm whales and sleeper sharks), while the remaining predators are limited to eating juveniles or young adults.[7]
[edit]Timeline
Main article: List of Colossal Squid specimens and sightings
- 1925 – Species was first discovered in the form of two tentacles found in the stomach of a sperm whale.[8]
- 1981 – A Russian trawler in the Ross Sea, off the coast of Antarctica, caught a large squid with a total length of 4 metres (13 ft), which was later identified as an immature female ofMesonychoteuthis hamiltoni.[9]
- 2003 – A complete specimen of a subadult female was found near the surface with a total length of 6 m (20 ft) and a mantle length of 2.5 m (8 ft).[10]
- 2005 – A specimen was captured at a depth of 1625 m while taking a toothfish from a longline off South Georgia Island. Although the mantle was not brought aboard, the mantle length was estimated at over 2.5 m, and the tentacles measured 230 cm. The animal is thought to have weighed between 150 and 200 kg.[11]
- 2007 – The largest recorded specimen was captured by a New Zealand fishing boat off Antarctica. It was initially estimated to measure 10 m (33 ft) in length and weigh 450 kg (992 lb). The squid was taken back to New Zealand for scientific study.[12] A study on the specimen later showed that its actual weight was 495 kg (1,091 lb), but that it only measured 4.2 m (14 ft) in total length as a result of the tentacles shrinking post mortem.[13]
[edit]Largest known specimen
See also: Cephalopod size
On February 22, 2007, it was announced by authorities in New Zealand that the largest known Colossal Squid had been captured. The specimen weighed 495 kg (1,091 lb) and was initially estimated to measure 10 m (33 ft) in total length. Fishermen on the vessel San Aspiring, owned by the Sanford seafood company, caught the animal in the freezing Antarctic waters of the Ross Sea. It was brought to the surface as it fed on an Antarctic toothfish that had been caught off a long line. It would not let go of its prey and could not be removed from the line by the fishermen, so they decided to catch it instead. They managed to envelop it in a net, hauled it aboard and froze it. The specimen eclipsed the previous largest find in 2003 by about 195 kilograms (430 lb),[14][15] although it is still considerably smaller than some estimates have predicted. The specimen was frozen in a cubic metre of water and transported to the Museum of New Zealand Te Papa Tongarewa, New Zealand's national museum.[16][17] Media reports suggested that scientists at the museum were considering using a giant microwave to defrost the squid because defrosting the squid at room temperatures would take days and it would be likely for the outside to rot while the core remained frozen.[18] However, they later opted for the more conventional approach of thawing the specimen in a bath of salt water.[19][20] After thawing, the squid measured only 4.2 m (14 ft) in total length, with the tentacles having shrunk significantly.[13] Although initially thought to be a male, closer inspection of the specimen showed it to be a female.[21]
[edit]Defrosting and dissection, April-May 2008
Thawing and dissection of the specimen took place at the Museum of New Zealand Te Papa Tongarewa[19] under the direction of senior biologist Chris Paulin, with technician Mark Fenwick, Dutch marine biologist and toxicologist Olaf Blaauw, AUT biologist Dr Steve O'Shea, Dr Tsunemi Kubodera, and AUT biologist Kat Bolstad.
Parts of the specimen have been examined:
- The beak is considerably smaller than some found in the stomachs of sperm whales,[22][23] suggesting there are Colossal Squid much larger than this one.[22][23]
- The eye is 27 cm (10.63 in) wide, with a lens 12 cm across. This is the largest eye of any known animal.[3] These measurements are of the partly collapsed specimen: when living the eye was probably 30[21] to 40 cm (12 to 16 in) across.[24]
- Inspection of the specimen with an endoscope revealed ovaries containing thousands of eggs.[21]
[edit]Exhibition
The Museum of New Zealand Te Papa Tongarewa is displaying this specimen in an exhibition which opened on December 13, 2008.[25] A website[26] on the squid specimen is also available.
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