Giant Squid


Wikipedia Article
Copyright Notice: This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Giant Squid".

Giant squid, once believed to be mythical creatures, are squid of the Architeuthidae family, represented by as many as eight species of the genus Architeuthis. They are deep-ocean dwelling animals that can grow to a tremendous size: recent estimates put the maximum size at 13 metres (43 ft) for females and 10 metres (33 ft) for males from caudal fin to the tip of the two long tentacles (second only to the colossal squid at an estimated 14 metres (46 ft), one of the largest living organisms). The mantle is only about 2 metres (7 ft) long (more for females, less for males), and the length of the squid excluding its tentacles is about 5 metres (16 ft). There have been claims reported of specimens of up to 20 metres (66 ft), but no animals of such size have been scientifically documented.

On September 30, 2004, researchers from the National Science Museum of Japan and the Ogasawara Whale Watching Association took the first images of a live giant squid in its natural habitat. Several of the 556 photographs were released a year later. The same team successfully filmed a live giant squid for the first time on December 4, 2006.

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.

The inside surfaces of the arms and tentacles are lined with hundreds of a sub-spherical suction cups, 2 to 5 centimetres (1 to 2 in) 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"). 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 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, which is 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 thanks to the ammonium chloride solution which 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 salmiakki 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
The giant squid is the second largest mollusc 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 18 m (59 ft) in length are widespread, but no animals approaching this size have been scientifically documented. According to giant squid expert Dr. Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands.

Based on the examination of 105 specimens and of beaks found inside sperm whales, giant squid's mantles are not known to exceed 2.25 m (7.4 ft) in length. Including the head and arms, but excluding the tentacles, the length very rarely exceeds 5 m (16 ft). Maximum total length, when measured relaxed post mortem, is estimated at 13 m (43 ft) for females and 10 m (33 ft) for males from caudal fin to the tip of the two long tentacles. Giant squid exhibit sexual dimorphism. Maximum weight is estimated at 275 kg (606 lb) for females and 150 kg (331 lb) for males.

 
 
Feeding:
Recent studies show that giant squid feed on deep-sea fish 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. Such fish as the Hoki are among the giant squid's diet.

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. 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 kg, that average 0.5-1.4 mm long and 0.3-0.7 mm 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 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.

Post-larval juveniles have been discovered in surface waters off New Zealand, and there are plans to capture more and maintain them in an aquarium to learn more about the creature.

Range and habitat
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.

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