Giant squid
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[Photo] Giant Squid, measuring 7m encased in ice in the Melbourne Aquarium.

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 10 meters (34 ft) for males and 13 meters (44 ft) for females from caudal fin to the tip of the two long tentacles (second only to the Colossal Squid at an estimated 14 meters (46 ft), one of the largest living organisms). The mantle length is only about 2 meters (7 ft) in length (more for females, less for males), and the length of the squid excluding its tentacles is about 5 meters (16 ft). In the past there were reported claims of specimens of up to 20 meters (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.[1] Several of the 556 photos were released a year later.

Biology
Despite their great length, giant squid are not particularly heavy when compared to their chief predator, the Sperm Whale, because the majority of their length is taken up by their eight arms and two tentacles. The weights of recovered specimens have been measured in hundreds, rather than thousands, of kilograms. Post-larval juveniles have been discovered in surface waters off New Zealand, and there are plans to capture more such juveniles and maintain them in an aquarium in an attempt to learn more about the creature's biology and habits.

The reproductive cycle of the giant squid is still a great mystery, but what has been learned so far is both bizarre and fascinating; male giant squid are equipped with a prehensile spermatophore-depositing tube, or penis, of over 3 feet (90 cm) in length, which extends from inside the animal's mantle and apparently is used to inject sperm-containing packets into the female squid's arms ??? how exactly the sperm then is transferred to the egg mass is a matter of much debate, but the recent recovery in Tasmania of a female specimen having a small subsidiary tendril attached to the base of each of its eight arms could be a vital clue in the solution of this enigma. The giant squid lacks the hectocotylus used for reproduction in many other cephalopods.

Giant squid possess the largest eyes of any living creature, with possible exception of those of the Colossal Squid, over 1 foot (30 cm) in diameter, and their arms are equipped with hundreds of suction cups in total; each is mounted on an individual "stalk" and equipped around its circumference with a ring of sharp teeth to aid the creature in capturing its prey by firmly attaching itself to it both by suction and perforation. The size of these suction cups can vary from 2 to 5 centimeters in diameter (1???2 in), and it is not uncommon to find their circular scars on the head area of sperm whales that have fed ??? or attempted to feed ??? upon giant squid. The only other known predator of the adult giant squid is the Pacific sleeper shark, found off Antarctica, but it is not yet known whether these sharks actively hunt the squid, or are simply scavengers of squid carcasses. Because sperm whales are skilled at locating giant squid, scientists have attempted to conduct in-depth observations of sperm whales in order to study squid.

One of the more unusual aspects of giant squid (as well as some other species of large squid) is their reliance upon the low density of ammonia in relation to seawater to maintain neutral buoyancy in their natural environment, as they lack the gas-filled swim bladder that fish use for this function; instead, they use ammonia (in the form of ammonium chloride) in the fluid of their flesh throughout their bodies, making it taste not unlike salmiakki. This makes the giant squid unattractive for general human consumption, although sperm whales seem to be attracted by (or are at least tolerant of) its taste.

Like all cephalopods they use special organs called statocysts to sense their orientation and motion in the water. The age of giant squids can be estimated by "growth rings" in the statocyst's "statolyth" much like counting tree rings. Much of what is known about these animals come from estimates based on these, and from undigested beaks found in sperm whale stomachs.

Species
The taxonomy of the giant squid, as with many cephalopod genera, has not been entirely resolved. Lumpers and splitters may propose as many as eight species or as few as one. The broadest list is:

Architeuthis dux, "Atlantic Giant Squid"
Architeuthis hartingii
Architeuthis japonica
Architeuthis kirkii
Architeuthis martensi
Architeuthis physeteris
Architeuthis sanctipauli, "Southern Giant Squid"
Architeuthis stockii
It is probable that not all of these are distinct species. No genetic or physical basis for distinguishing between the named species 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.

In the 1984 FAO Species Catalogue of the Cephalopods of the World, C.F.E. Rope, M.J. Sweeney and C.F. Nauen wrote:

"Many species have been named in the sole genus of the family Architeuthidae, but they are so inadequately described and poorly understood that the systematics of the group is thoroughly confused."

Kir Nazimovich Nesis (1982, 1987) considers that only three species are likely to be valid.

In 1991, Frederick Aldrich of the Memorial University of Newfoundland wrote:

"I reject the concept of 20 separate species, and until that issue is resolved, I choose to place them all in synonymy with Architeuthis dux Steenstrup."

In a letter to Richard Ellis dated June 18, 1996, Martina Roeleveld of the South African Museum wrote:

"So far, I have seen nothing to suggest that there might be more than one species of Architeuthis."

In Cephalopods: A World Guide (2000), Mark Norman writes the following:

"The number of species of giant squid is not known although the general consensus amongst researchers is that there are at least three species, one in the Atlantic Ocean (Architeuthis dux), one in the Southern Ocean (A. santipauli) and at least one in the northern Pacific Ocean (A. martensi)."

http://en.wikipedia.org/wiki/Giant_squid

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