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The giant squid (genus ''Architeuthis'') is a deep-ocean dwelling squid in the family Architeuthidae. Giant squid can grow to a tremendous size due to deep-sea gigantism: recent estimates put the maximum size at for females and for males from the posterior fins to the tip of the two long tentacles (second only to the colossal squid at an estimated ,〔Anderton, H.J. 2007. (Amazing specimen of world's largest squid in NZ ). New Zealand Government website.〕 one of the largest living organisms). The mantle is about long (more for females, less for males), and the length of the squid excluding its tentacles (but including head and arms) rarely exceeds . Claims of specimens measuring or more have not been scientifically documented. The number of different giant squid species has been debated, but recent genetic research suggests that only one species exists.〔 In 2004 Japanese researchers took the first images of a live giant squid in its natural habitat, and in July 2012 a live adult was first filmed in its natural habitat off Chichi-jima. == 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 arm and tentacle is divided into three regions – carpus ("wrist"), manus ("hand") and dactylus ("finger").〔Young, R.E., M. Vecchione & K.M. Mangold (2001). (Tentacular Club Variation in Cephalopods ). Tree of Life web project.〕〔Young, R.E., M. Vecchione & K.M. Mangold (2000). (Cephalopod Tentacle Terminology ). Tree of Life web project.〕 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. Giant squid have small fins at the rear of their mantles used for locomotion. Like other cephalopods, they are propelled by jet – 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 used to deter predators. 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 colour, but it can probably discern small differences in tone, which is important in the low-light conditions of the deep ocean.〔Piper, R. (2007). ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals''. Greenwood Press.〕 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 ''salmiakki'' 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Giant squid」の詳細全文を読む スポンサード リンク
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