Giant squid

Giant squid
Giant squid, Architeuthis sp., modified from an illustration by A.E. Verrill, 1880.
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclass: Coleoidea Order: Teuthida Suborder: Oegopsina Family: Architeuthidae Pfeffer, 1900 Genus: Architeuthis Steenstrup in Harting, 1860
Species
Architeuthis dux Steenstrup, 1857 ?Architeuthis hartingii Verrill, 1875 ?Architeuthis japonica Pfeffer, 1912 ?Architeuthis kirkii Robson, 1887 ?Architeuthis martensi (Hilgendorf, 1880) ?Architeuthis physeteris (Joubin, 1900) ?Architeuthis sanctipauli (Velain, 1877) ?Architeuthis stockii (Kirk, 1882)
Synonyms
Architeuthus Steenstrup, 1857 Dinoteuthis More, 1875 Dubioteuthis Joubin, 1900 Megaloteuthis Kent, 1874 Megateuthis Hilgendorf in Carus, 1880 Megateuthus Hilgendorf, 1880 Mouchezis Velain, 1877 Plectoteuthis Owen, 1881 Steenstrupia Kirk, 1882

Giant squid is the common name for any of the very large squid comprising the genus Architeuthis of the cephalopod family Architeuthidae, characterized by very long arms and tentacles, small and ovoid fins, and a distinctive tentacular club structure. These are the second largest known mollusks and possibly the second largest invertebrates ever to live in the oceans. The number of valid species is difficult to access, as many claimed species have been described from a single, incomplete specimen. Generally, from three to eight species are recognized, although some authorities recognize only one species, A. dux.

Giant squid can grow to a tremendous size. Recent estimates put the maximum size at 13 meters (43 ft) for females and 10 meters (33 ft) for males from caudal fin to the tip of the two long tentacles (second only to the colossal squid). The mantle is about 2 meters (6.6 ft) long (more for females, less for males), and the length of the squid excluding its tentacles is about 5 meters (16 ft). There have been claims reported of specimens of up to 20 meters (66 ft) in total length, but no animals of such size have been scientifically documented.

The elusive nature of the giant squid and its terrifying appearance have firmly established its place in the human imagination. Representations of the giant squid have been known from early legends of the Kraken through books such as Moby-Dick and Twenty Thousand Leagues Under the Sea to modern animated television programs. In particular, the image of a giant squid locked in battle with a sperm whale is a common one, although the squid is, in fact, the whale's prey and not an equal combatant. With the vast amount of eggs produced by giant squids—one female was found with over one million eggs—the giant squid, though rarely seen, surely plays an integral role in food chains in the depths of the oceans.

Anatomy

Like all squid, a giant squid has a mantle (torso), eight arms, and two longer tentacles. The arms and tentacles account for much of the squid's great length, so giant squid are much lighter than their chief predators, sperm whales. Scientifically documented specimens have weighed hundreds, rather than thousands, of kilograms.

Tentacular club of Architeuthis

Giant squid have very long arms and exceptionally long tentacles, and the tentacles have a distinctive club structure (Roper 1998). The inside surfaces of the arms and tentacles are lined with hundreds of sub-spherical suction cups, 2 to 5 centimeters (0.79 to 2.0 in) in diameter, each mounted on a stalk. The circumference of these suckers is lined with sharp, finely serrated rings of chitin (Roeleveld 2002). The perforation of these teeth and the suction of the cups serve to attach the squid to its prey. It is common to find circular scars from the suckers on or close to the head of sperm whales that have attacked giant squid. Each arm and tentacle is divided into three regions—carpus ("wrist"), manus ("hand") and dactylus ("finger") (Young et al. 2000, 2001). The carpus has a dense cluster of cups, in six or seven irregular, transverse rows. The manus is broader, close to the end of the arm, and has enlarged suckers in two medial rows. The dactylus is the tip. The bases of all the arms and tentacles are arranged in a circle surrounding the animal's single parrot-like beak, as in other cephalopods.

A piece of sperm whale skin with giant squid sucker scars.

Giant squid have small ovoid fins at the rear of the mantle used for locomotion. Like other cephalopods, giant squid are propelled by jet—by pushing water through its mantle cavity through the funnel, in gentle, rhythmic pulses. They can also move quickly by expanding the cavity to fill it with water, then contracting muscles to jet water through the funnel. Giant squid breathe using two large gills inside the mantle cavity. The circulatory system is closed, a distinct characteristic of cephalopods. Like other squid, they contain dark ink used to deter predators.

Giant squid have a sophisticated nervous system and complex brain, attracting great interest from scientists. They also have the largest eyes of any living creature except perhaps colossal squid—over 30 centimeters (1 ft) in diameter. Large eyes can better detect light (including bioluminescent light), which is scarce in deep water.

Giant squid and some other large squid species maintain neutral buoyancy in seawater through an ammonium chloride solution that flows throughout their body and is lighter than seawater. This differs from the method of flotation used by fish, which involves a gas-filled swim bladder. The solution tastes somewhat like salty liquorice and makes giant squid unattractive for general human consumption.

Like all cephalopods, giant squid have organs called statocysts to sense their orientation and motion in water. The age of a giant squid can be determined by "growth rings" in the statocyst's "statolith," similar to determining the age of a tree by counting its rings. Much of what is known about giant squid age is based on estimates of the growth rings and from undigested beaks found in the stomachs of sperm whales.

Size

Giant squid measuring over 4 meters without its two long feeding tentacles.

The giant squid is the second largest mollusk and the second largest of all extant invertebrates. It is only exceeded in size by the colossal squid, Mesonychoteuthis hamiltoni, which may have a mantle nearly twice as long. Several extinct cephalopods, such as the Cretaceous vampyromorphid Tusoteuthis, and the Ordovician nautiloid Cameroceras may have grown even larger.

Yet, giant squid size, particularly total length, has often been misreported and exaggerated. Reports of specimens reaching and even exceeding 20 meters (66 ft) in length are widespread, but no animals approaching this size have been scientifically documented (O'Shea and Bolstad 2008). According to giant squid expert Dr. Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands (O'Shea and Bolstad 2008).

Based on the examination of 130 specimens and of beaks found inside sperm whales, giant squid's mantles are not known to exceed 2.25 meters (7.4 ft) in length (O'Shea and Bolstad 2008). Including the head and arms, but excluding the tentacles, the length very rarely exceeds 5 meters (16 ft) (O'Shea and Bolstad 2008). Maximum total length, when measured relaxed post mortem, is estimated at 13 meters (43 ft) for females and 10 meters (33 ft) for males from caudal fin to the tip of the two long tentacles (O'Shea and Bolstad 2008). Giant squid exhibit reverse sexual dimorphism. Maximum weight is estimated at 275 kilograms (610 lb) for females and 150 kilograms (330 lb) for males (O'Shea and Bolstad 2008).

Distribution and habitat

Worldwide giant squid distribution based on recovered specimens.

Giant squid are very widespread, occurring in all of the world's oceans. They are usually found near continental and island slopes from the North Atlantic Ocean, especially Newfoundland, Norway, the northern British Isles, and the oceanic islands of the Azores and Madeira, to the South Atlantic around southern Africa, the North Pacific around Japan, and the southwestern Pacific around New Zealand and Australia. Specimens are rare in tropical and polar latitudes.

Most records are from sperm whale stomachs, strandings, and floaters so it is difficult to access the vertical distribution, but indirect evidence suggests a deep-sea habitat (Roper 1998).

Feeding

Recent studies show that giant squid feed on deep-sea fish and other squid species (Bolstad and O'Shea 2004). They catch prey using the two tentacles, gripping it with serrated sucker rings on the ends. Then they bring it toward the powerful beak, and shred it with the radula (tongue with small, file-like teeth) before it reaches the esophagus. They are believed to be solitary hunters, as only individual giant squid have been caught in fishing nets. Although the majority of giant squid caught by trawl in New Zealand waters have been associated with the local hoki (Macruronus novaezelandiae) fishery, the fish themselves do not feature in the squid's diet. This suggests that giant squid and hoki prey on the same animals (Bolstad and O'Shea 2004).

Adult giant squids' only known predators are sperm whales and possibly Pacific sleeper sharks, found off Antarctica, but it is unknown whether these sharks hunt squid, or just scavenge squid carcasses. It has also been suggested that pilot whales may feed on giant squid (Soto et al. 2008; Walker 2008). Juveniles are preyed on by deep sea sharks and fishes. Because sperm whales are skilled at locating giant squid, scientists have tried to observe them to study the squid.

Reproductive cycle

Little is known about the reproductive cycle of giant squid. It is thought that they reach sexual maturity at about 3 years; males reach sexual maturity at a smaller size than females. Females produce large quantities of eggs, sometimes more than 5 kilograms, that average 0.5 to 1.4 millimeters (0.020 to 0.055 in) long and 0.3 to 0.7 millimeters (0.012 to 0.028 in) wide. One female was found that had well in excess of a million eggs in her ovary (Roper 1998). Females have a single median ovary in the rear end of the mantle cavity and paired convoluted oviducts where mature eggs pass exiting through the oviducal glands, then through the nidamental glands. As in other squid, these glands produce a gelatinous material used to keep the eggs together once they are laid.

In males, as with most other cephalopods, the single, posterior testis produces sperm that move into a complex system of glands that manufacture the spermatophores. These are stored in the elongate sac, or Needham's sac, that terminates in the penis from which they are expelled during mating. The penis is prehensile, over 90 centimeters long, and extends from inside the mantle.

How the sperm is transferred to the egg mass is much debated, as giant squid lack the hectocotylus used for reproduction in many other cephalopods. It may be transferred in sacs of spermatophores, called spermatangia, which the male injects into the female's arms. This is suggested by a female specimen recently found in Tasmania, having a small subsidiary tendril attached to the base of each arm.

Classification

The taxonomy of the giant squid, as with many cephalopod genera, has not been resolved. Diverse species of Architeuthis have been proposed, often with the species described from a single specimen that was found floating on the surface, stranded on shore, or in the stomach of a sperm whale, and thus only consisted of parts of the animal (Roper 1998). Based on this, some have claimed as many as 20 species, and at one time even eight different genera were created, which are now synonyms of Architeuthis. Architeuthis currently is the sole genus of the cephalopod family Architeuthidae (ITIS 1999b).

Lumpers and splitters today may propose as many as eight species or as few as one. The broadest list is (ITIS 1999a):

• Architeuthis dux, "Atlantic giant squid"
• Architeuthis hartingii
• Architeuthis japonica
• Architeuthis kirkii
• Architeuthis martensi, "North Pacific giant squid"
• Architeuthis physeteris
• Architeuthis sanctipauli, "Southern giant squid"
• Architeuthis stockii

Architeuthis sanctipauli was described in 1877 based on a specimen found washed ashore in Île Saint-Paul three years earlier.

It is probable that not all of these are distinct species. No genetic or physical basis for distinguishing between them has been proposed, as evidenced by the placenames—of location of specimen capture—used to describe several of them. The rarity of observations of specimens and the extreme difficulty of observing them alive, tracking their movements, or studying their mating habits militates against a complete understanding.

Some consider only one species to be valid, A. dux, with all others being at most subspecies (Aldrich 1992; Ellis 1998). Others consider that perhaps three valid species exist: A. dux in the North Atlantic Ocean, A. sanctipuali in the Southern Ocean, and A. martensi in the North Pacific (Roper 1998; Nesis 1982; Nesis and Burgess 1987; Norman 2000).

History of sightings and mythologies

Aristotle, who lived in the fourth century B.C.E., already described a large squid, which he called teuthus, distinguishing it from the smaller squid, the teuthis. He mentions that "of the calamaries the so-called teuthus is much bigger than the teuthis; for teuthi [plural of teuthus] have been found as much as five ells long."

Pliny the Elder, living in the first century C.E., also described a gigantic squid in his Natural History, with the head "as big as a cask," arms 30 feet (9.1 m) long, and carcass weighing 700 pounds (320 kg) (Pliny, Ellis 1998).

Tales of giant squid have been common among mariners since ancient times, and may have led to the Norwegian legend of the kraken, a tentacled sea monster as large as an island capable of engulfing and sinking any ship. Japetus Steenstrup, the describer of Architeuthis, suggested a giant squid was the species described as a sea monk to the Danish king Christian III c.1550. The Lusca of the Caribbean and Scylla in Greek mythology may also derive from giant squid sightings. Eyewitness accounts of other sea monsters like the sea serpent are also thought to be mistaken interpretations of giant squid.

The Alecton attempts to capture a giant squid in 1861

Steenstrup wrote a number of papers on giant squid in the 1850s. He first used the term "Architeuthus" (this was the spelling he chose) in a paper in 1857. A portion of a giant squid was secured by the French gunboat Alecton in 1861 leading to wider recognition of the genus in the scientific community. From 1870 to 1880, many squid were stranded on the shores of Newfoundland. For example, a specimen washed ashore in Thimble Tickle Bay, Newfoundland on November 2, 1878; its mantle was reported to be 6.1 meters (20 ft) long, with one tentacle 10.7 meters (35 ft) long, and it was estimated as weighing 2.2 metric tons. In 1873, a squid "attacked" a minister and a young boy in a dory in Bell Island, Newfoundland. Many strandings also occurred in New Zealand during the late nineteenth century.

Giant squid from Logy Bay, Newfoundland in Reverend Moses Harvey's bathtub, November/December, 1873

Although strandings continue to occur sporadically throughout the world, none have been as frequent as those at Newfoundland and New Zealand in the nineteenth century. It is not known why giant squid become stranded on shore, but it may be because the distribution of deep, cold water where squid live is temporarily altered. Many scientists who have studied squid mass strandings believe that they are cyclical and predictable. The length of time between strandings is not known, but was proposed to be 90 years by Architeuthis specialist Frederick Aldrich. Aldrich used this value to correctly predict a relatively small stranding that occurred between 1964 and 1966.

The search for a live Architeuthis specimen includes attempts to find live young, including larvae. The larvae closely resemble those of Nototodarus and Moroteuthis, but are distinguished by the shape of the mantle attachment to the head, the tentacle suckers, and the beaks.

Twenty-first century sightings

An illustration from the original edition of Twenty Thousand Leagues Under the Sea depicting a giant squid.

The first footage of live larval giant squid ever captured on film was in 2001. As of 2004, almost 600 giant squid specimens had been reported (Guerra et al. 2004).

The first photographs of a live giant squid in its natural habitat were taken on September 30, 2004, by Tsunemi Kubodera (National Science Museum of Japan) and Kyoichi Mori (Ogasawara Whale Watching Association). Their teams had worked together for nearly two years to accomplish this. They used a five-ton fishing boat and only two crew members. The images were created on their third trip to a known sperm whale hunting ground 970 kilometers (600 miles) south of Tokyo, where they had dropped a 900 meters (3,000 ft) line baited with squid and shrimp. The line also held a camera and a flash. After over 20 tries that day, an 8 meters (26 ft) giant squid attacked the lure and snagged its tentacle. The camera took over 500 photos before the squid managed to break free after four hours. The squid's 5.5 meters (18 ft) tentacle remained attached to the lure. Later DNA tests confirmed the animal as a giant squid (Kubodera and Mori 2005).

On September 27, 2005, Kubodera and Mori released the photographs to the world. The photo sequence, taken at a depth of 900 meters off Japan's Ogasawara Islands, shows the squid homing in on the baited line and enveloping it in "a ball of tentacles." The researchers were able to locate the likely general location of giant squid by closely tailing the movements of sperm whales. According to Kubodera, "we knew that they fed on the squid, and we knew when and how deep they dived, so we used them to lead us to the squid." Kubodera and Mori reported their observations in the journal Proceedings of the Royal Society.

Among other things, the observations demonstrate actual hunting behaviors of adult Architeuthis, a subject on which there had been much speculation. The photographs showed an aggressive hunting pattern by the baited squid, leading to it impaling a tentacle on the bait ball's hooks. This may disprove the theory that the giant squid is a drifter that eats whatever floats by, rarely moving so as to conserve energy. It seems that the species has a much more active feeding technique.

In December 2005, the Melbourne Aquarium in Australia paid AUD$100,000 (around £47,000GBP or $90,000US) for the intact body of a giant squid, preserved in a giant block of ice, which had been caught by fishermen off the coast of New Zealand's South Island that year (Hokroyd 2005).

In early 2006, another giant squid was caught off the coast of the Falkland Islands by a trawler. It was 8.62 meters (28.3 ft} long and was sent to the Natural History Museum in London to be studied and preserved. It was put on display on March 1, 2006 at the Darwin Centre (Jha 2006). The find of such a large, complete specimen is very rare, as most specimens are in a poor condition, having washed up dead on beaches or been retrieved from the stomach of dead sperm whales.

On December 4, 2006, an adult giant squid was finally caught on video by Kubodera near the Ogasawara Islands, 1,000 kilometers (620 mi) south of Tokyo. It was a small female about 3.5 meters (11 ft) long and weighing 50 kilograms (110 lb). It was pulled aboard the research vessel but died in the process (Reuters 2006).

References

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• Aldrich, F. A.,and E. L. Brown. 1967. The giant squid in Newfoundland. The Newfoundland Quarterly. 65(3): 4–8.

• Aristotle. n.d. Historia animalium. Internet Classics Archive. Retrieved October 22, 2008.

• Associated Press (AP). 2006. Japanese researchers capture giant squid. Foxnews.com December 22, 2006. Retrieved October 22, 2008.

• BBC. 2003. Giant squid attacks French boat. BBC January 15, 2003. Retrieved October 22, 2008.

• Bolstad, K. S., and S. O'Shea. 2004. Gut contents of a giant squid Architeuthis dux (Cephalopoda: Oegopsida) from New Zealand waters. New Zealand Journal of Zoology 31: 15–21. Retrieved October 22, 2008.

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