Scientists have discovered an animal called a siphonophore in Australia that could be the longest ever seen.

Siphonophores are deep-sea predators made up of an array of small clones that act together as one.

The string-like creature measured an estimated 150 feet in length — almost twice as long as a blue whale.

It was discovered by the US-based Schmidt Ocean Institute (SOI) during a deep-sea expedition into the Ningaloo Canyons.

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Scientists exploring the deep waters off Australia's western coast have discovered what may be the longest animal ever seen, along with up to 30 new marine species.

The discovery of the siphonophore measuring an estimated 150 feet (46 metres) - twice as long as many blue whales - came as part of an expedition into the Ningaloo Canyons led by the US-based Schmidt Ocean Institute (SOI).

"We think it's the longest animal recorded to date," SOI director of marine communications Carlie Wiener told USA Today.

Siphonophores are deep-sea predators made up of an array of small clones that act together as one.

They appear to spread out like a single string and, similar to jellyfish, feed by dangling stinging tentacles out into surrounding water.

Nerida Wilson, a senior research scientist at the Western Australia Museum, who led the expedition, described the discovery of the extra-long creature as an "amazing sight".

"Like a giant UFO," she said in a post on Twitter last week. "What amazing creatures live in our oceans."

The SOI's research vessel plunged to depths of nearly 4,500 metres, but the siphonophore was only spotted as the vehicle was making its way back to the surface.

"Most scientists had drifted out of the control room," Wilson told The Guardian.

"The word soon spread and people came pouring into the control room to share the excitement.

"We couldn't believe what we were seeing."

Commenting on the finding of several new species, she added the team had been keen to "reveal the incredible biodiversity that is there".

"We were definitely looking for and expecting new species," she said. "Those waters were just too unexplored to not yield such treasures."

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