The creature, which is as long as a London bus from tentacle tip to tail, has been filmed by Japanese researchers using a baited underwater camera, shedding new light on the lifestyle of one of nature’s most enigmatic living wonders.

The first observed specimen measured about 26ft (8m) in total, with 16ft tentacles. Even so, it was something of a titch by the standards of the species as a whole, with the largest yet washed ashore, in New Zealand — at 59ft — more than twice as big.

The giant squid, Architeuthis dux, has been known since the 16th century from dead specimens washed up on beaches or snared by fishermen’s nets, and from the occasional fleeting sighting when it has neared the surface. But it had never before been seen in its natural deep-water environment.

Its size, fearsome tentacles and beak have captured the imaginations of sailors and writers, for whom it has become an emblem of the terrors of the deep. In Jules Verne’s 20,000 Leagues Under the Sea, Captain Nemo’s submarine Nautilus was attacked by a “squid of colossal dimensions” that almost destroyed the vessel.

Occasional attacks on shipping have been reported, most recently in 2003 when a yacht skippered by Olivier de Kersauson was gripped during a round-the-world race.

Giant squid have also been found in the stomachs of sperm whales, which feed on the creatures, after what must be underwater heavyweight wrestling bouts. Giant squid beaks have been found inside sperm whales, which have in turn been found sporting huge tentacle-inflicted wounds. Almost nothing, however, is known about where and how Architeuthis feeds, or about how it behaves in its natural habitat.

That has now changed, after Tsunemi Kudobera of the National Science Museum and Kyoichi Mori of the Ogasawara Whale Watching Association used sperm whale migration patterns to guide them to the best place to watch for giant squid.

Whale watchers in the Ogasawara Islands, to the south of Japan in the north Pacific, have long known that sperm whales tend to gather near a steep continental shelf about six miles off Chichijima Island. Tagging of the whales showed that they dive to depths of about 3,250ft (1,000m) where giant squid are thought to lurk.

The team devised a rig at this spot comprising a camera, light and data logger attached to two baited hooks, each carrying a bag of mashed shrimps. Pictures were taken every 30 seconds over a five-hour period.

At 9.15am on September 30 last year, a 26ft squid started to lunge at the lower of the two bait bags, 2,925ft (900m) below the surface. As it did so, it impaled one of its tentacles on the hook, becoming trapped.

Over the next four hours, the squid was photographed every 30 seconds as it struggled to free itself, eventually escaping only when part of its trapped tentacle was severed.

The photographs are not only the first taken of a living giant squid, but also show how the creatures propel themselves and attack their prey. “Architeuthis appeared to be a much more active predator than previously suspected, using its elongated feeding tentacles to strike and tangle prey,” the researchers said. “It appears that the tentacles coil into an irregular ball in much the same way that pythons rapidly envelop their prey within coils of their body immediately after striking.”

The squid appears to attack its prey head-on, approaching horizontally rather than from above or below. The observations are published in the journal Proceedings of the Royal Society.

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