Inky the octopus, who escaped from an aquarium in Napier, New Zealand. Photo: Stuff.co.nz

It was an audacious nighttime escape.

After busting through an enclosure, the nimble contortionist quietly crossed the floor, slithered through a narrow drain hole about 15 centimetres in diameter and jumped into the sea. Then he disappeared without a trace.

This was no Houdini, but rather a common New Zealand octopus called Inky, about the size of a soccer ball.

The breakout at the National Aquarium of New Zealand in Napier, which has captured the imagination of New Zealanders and made headlines around the world, apparently began when Inky slipped through a small gap at the top of his tank.

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Octopus tracks suggest he then scampered across the floor and slid down a 50 metre long drainpipe that dropped him into Hawke's Bay, on the east coast of North Island, according to reports in New Zealand's news media.

The aquarium's keepers noticed the escape when they came to work and discovered that Inky was not in his tank. A less independence-minded octopus, Blotchy, remained behind.

The aquarium's manager, Rob Yarrall, told Radio New Zealand that employees had searched the aquarium's pipes after discovering Inky's trail, to no avail.

The escape happened several months ago, but only recently came to light. "He managed to make his way to one of the drain holes that go back to the ocean, and off he went," Yarrall said. "Didn't even leave us a message."

Inky's escape surprised few in the world of marine biology, where octopuses are known for their strength, dexterity and intelligence.

Alix Harvey, an aquarist at the Marine Biological Association in England, noted that octopuses, members of a class of marine animals including squid and cuttlefish called Cephalopoda, have shown themselves to be adept at escaping through spaces as small as a coin, constrained only by their beaks, the only inflexible part of their bodies.

Harvey said that octopuses had also been documented opening jars, sneaking through tiny holes on boats, and that they could deflect predators by spraying an ink that lingers in the water and acts as a decoy. Some have been seen hauling coconut shells to build underwater shelters.

"Octopuses are fantastic escape artists," she said. "They are programmed to hunt prey at night and have a natural inclination to move around at night."

She continued, "They have a complex brain, have excellent eyesight, and research suggests they have an ability to learn and form mental maps."

Harvey recalled one wily octopus at a British aquarium that escaped nightly from his tank, slithered to a nearby tank to snack on fish for dinner, and returned home.

Octopuses' intelligence, she said, was partly an evolutionary response to their habitation in complex environments such as coral reefs, in which the animals need to hide from predators and sneak up on their prey.

The New York Times