QUnderwater explorers have videoed a strange and record-breaking organism in a deep ocean canyon off Australia.

The string-like creature, which was introduced to the internet by the Schmidt Ocean Institute (SOI) on Twitter April 6, is estimated to have an outer ring 154 feet long — the size of an 11-story building — and a possible total length of more than 390 feet, Newsweek reported.

Nerida Wilson couldn’t take her eyes off the computer screen. Some 2,000 feet beneath the research boat she was aboard, a creature drifted past in the shape of a vast, galactic swirl. By her team’s estimates, it was 150 feet long.

“It looked like an incredible U.F.O.,” said Dr. Wilson, a senior research scientist at the Western Australian Museum.

She and her colleagues documented this organism with the help of SuBastian, a remotely piloted deep-sea robot, during a March expedition on the Falkor, a research vessel operated by the Schmidt Ocean Institute. Their mission was to understand what lives in the deep waters off Australia’s western edge. And the coiling stringy mass they had just found was a siphonophore, the first spotted off Western Australia and potentially the longest organism in the sea.

The longest previously known marine creature is the lion’s mane jellyfish — its tentacles can be up to 120 feet long. By comparison, blue whales, while the most massive creatures ever to have lived, are nearly 100 feet long.

Each siphonophore is a colony of individual zooids, clusters of cells that clone themselves thousands of times to produce an extended, stringlike body. While some of her colleagues compared the siphonophore to silly string, Dr. Wilson said the organism is much more organized than that.

The team aboard the Falkor captured 181 hours of footage during its trip, including the images of the spiraling siphonophore. The SuBastian underwater robot also brought back samples of deep-sea creatures living in Australian waters nearly 15,000 feet down, in Cape Range and Cloates Canyons.

“What’s fascinating about this particular part of the world is that it has not been explored,” said Jyotika Virmani, executive director of the Schmidt Ocean Institute. “Any time people go down into the deep sea, it’s so vast and yet so unexplored that it’s very easy to make new discoveries and to see something we’ve never seen before. It is like being on a new planet.”