The giant squid (Architeuthis dux) is a species of deep-ocean dwelling squid in the family Architeuthidae. It can grow to a tremendous size, offering an example of abyssal gigantism; recent estimates put the maximum body size at around for females, with males slightly shorter, from the posterior fins to the tip of its long arms. This makes it longer than the colossal squid at an estimated , but substantially lighter, as it is less robust and its arms make up much of the length. The mantle of the giant squid is about long (longer for females, shorter for males), and the feeding tentacles of the giant squid, concealed in life, are . Claims of specimens measuring or more have not been scientifically documented.Tracey, D. M., O. F. Anderson & J. R. Naylor (2011). A guide to common deepsea invertebrates in New Zealand waters. Third edition. National Institute of Water and Atmospheric Research, Wellington. 317 pp.Yukhov, V. L. (2014). Гигантские кальмары рода Architeuthis в Южном океане / Giant calmaries Architeuthis in the Southern ocean . [Gigantskiye kalmary roda Architeuthis v Yuzhnom okeane.] Ukrainian Antarctic Journal no. 13: 242–253.
The number of different giant squid species has been debated, but genetic research suggests that only one species exists. In 2004, a Japanese research team obtained the first images of a living specimen in its habitat.
Taxonomy The closest relatives of the giant squid are thought to be the four obscure species of "neosquid" in the family Neoteuthidae, each of which belongs to its own monotypic genus, as with the giant squid. Together, both families comprise the superfamily Architeuthoidea.
Range and habitat The giant squid is widespread, occurring in all of the world's oceans. It is usually found near continental and island slopes from the North Atlantic Ocean, especially Newfoundland, Norway, the northern British Isles, Spain, 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.
The vertical distribution of giant squid is incompletely known, but data from trawled specimens and sperm whale diving behavior suggest it spans a large range of depths, possibly .
Morphology and anatomy
Like all squid, a giant squid has a mantle (torso), eight arms, and two longer tentacles (the longest known tentacles of any cephalopod). The arms and tentacles account for much of the squid's great length, making it much lighter than its chief predator, the sperm whale. Scientifically documented specimens have masses of hundreds, rather than thousands, of kilograms.
The inside surfaces of the arms and tentacles are lined with hundreds of subspherical suction cups, in diameter, each mounted on a stalk. The circumference of these suckers is lined with sharp, finely serrated rings of chitin. 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 tentacular club is divided into three regions—the carpus ("wrist"), manus ("hand") and dactylus ("finger"). The carpus has a dense cluster of cups, in six or seven irregular, transverse rows. The manus is broader closer to the end of the club, 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.
Giant squid have small fins at the rear of their mantles used for locomotion. Like other cephalopods, they move through jet propulsion—by pulling water into the mantle cavity, and pushing it through the siphon, 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 siphon. Giant squid breathe using two large gills inside the mantle cavity. The circulatory system is closed, which is a distinct characteristic of cephalopods. Like other squid, they contain dark ink.
The giant squid has a sophisticated nervous system and complex brain, attracting great interest from scientists. It also has the largest eyes of any living creature except perhaps the colossal squid—up to at least in diameter, with a pupil (only the extinct ichthyosaurs are known to have had larger eyes). Large eyes can better detect light (including bioluminescent light), which is scarce in deep water. The giant squid probably cannot see color, but it can probably discern small differences in tone, which is important in the low-light conditions of the deep ocean.
Giant squid and some other large squid species maintain neutral buoyancy in seawater through an ammonium chloride solution which is found throughout their bodies and is lighter than seawater. This differs from the method of flotation used by most fish, which involves a gas-filled swim bladder. The solution tastes somewhat like salty liquorice/salmiak and makes giant squid unattractive for general human consumption.
Like all cephalopods, giant squid use 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
The giant squid is the second-largest mollusc and one of the largest of all extant invertebrates. It is exceeded only by the colossal squid, Mesonychoteuthis hamiltoni, which may have a mantle nearly twice as long. Several extinct cephalopods, such as the Cretaceous coleoids Yezoteuthis and Haboroteuthis, and the Ordovician nautiloid Endoceras may have grown even larger. Although the Cretaceous Tusoteuthis, with its long mantle, was once considered to grow to a size close to that of the giant squid (over including arms), this genus is likely doubtful. The largest specimen probably belonged to the genus Enchoteuthis, estimated to have short arms, with a total length of only .
Giant squid size, particularly total length, has often been exaggerated. Reports of specimens reaching and even exceeding are widespread, but no specimens approaching this size have been scientifically documented. According to giant squid expert Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands.
Based on the examination of 130 specimens and of beaks found inside sperm whales, giant squids' mantles are not known to exceed . Including the head and arms, but excluding the tentacles, the length very rarely exceeds . Maximum total length, when measured relaxed post mortem, is estimated at or for females and for males from the posterior fins to the tip of the two long tentacles.
Giant squid exhibit sexual dimorphism. Maximum weight is estimated at for females and for males.
Reproductive cycle Little is known about the reproductive cycle of giant squid. They are thought to reach sexual maturity at about three years old; males reach sexual maturity at a smaller size than females. Females produce large quantities of eggs, sometimes more than , that average long and wide. 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 long, and extends from inside the mantle. The two ventral arms on a male giant squid are hectocotylized, which means they are specialized to facilitate the fertilization of the female's eggs.
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.
Post-larval juveniles have been discovered in surface waters off New Zealand, with plans to capture more and maintain them in an aquarium. Young giant squid specimens were found off the coast of southern Japan in 2013 and confirmed through genetic analysis.
Another juvenile, approximately long, was encountered and filmed alive in the harbour in the Japanese city of Toyama on 24 December 2015; after being filmed and viewed by a large number of spectators, including a diver who entered the water to film the squid up close, it was guided out of the harbour into Toyama Bay by the diver.
Genetics Analysis of the mitochondrial DNA of giant squid individuals from all over the world has found that there is little variation between individuals across the globe (just 181 differing genetic base pairs out of 20,331). This suggests that there is only a single species of giant squid in the world. Squid larvae may be dispersed by ocean currents across vast distances.
Ecology Feeding
Recent studies have shown giant squid feed on deep-sea fish, such as the orange roughy (Hoplostethus atlanticus), and other squid species. 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, hoki do not feature in the squid's diet. This suggests giant squid and hoki prey on the same animals.
Predators and potential cannibalism