Underwater explorers found the 150 foot (46 metre) long UFO-like creature, known as a siphonophore, in the deep sea canyons near Ningaloo reef in Western Australia. (SWNS)

The longest creature to have ever lived has been discovered in ocean depths off the coast of Western Australia.

Underwater explorers found the 150 foot (46 metre) long “UFO-like” creature, known as a siphonophore, in the deep sea canyons near the Ningaloo reef.

Researchers used ROV SuBastian, an underwater robot, to complete 20 dives at depths of 14,764 feet (4.5 km) over a period of 181 hours.

Scientists spotted the swirling siphonophore – a floating stringy creature made up of tiny zooids – deep in the Indian Ocean.

Researchers used an underwater robot called ROV SuBastian to complete 20 dives at depths of 14,764 feet (4,500 metres) over a 181-hour period. (Getty)

The creature is said to be well over the length of blue whales, which themselves can reach up to 100 feet (30 metres) in length

The Schmidt Ocean Institute tweeted a video of the creature describing it as “beautiful” and “UFO-like”.

But the discovery of the giant gelatinous string wasn’t the only unique find. Experts also discovering 30 new underwater species of some of the deepest fish and marine invertebrates ever documented in the region.

They found large communities of glass sponges in Cape Range Canyon and collected the first giant hydroids – enormously long feathery colonies – in Australia.

And for the first time in Western Australia, scientists found the bioluminescent Taning’s octopus squid, long-tailed sea cucumber and other molluscs, barnacle and squat lobster species.

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Chief scientist Dr Nerida Wilson, from the Western Australia Museum, said: “We suspected these deep sea areas would be diverse but we have been blown away by the significance of what we have seen.”

The research was a collaboration between the Western Australia Museum, Curtin University in Perth, Geoscience Australia, Scripps Institution of Oceanography and the Schmidt Ocean Institute.

And the expedition was part of a year-long initiative in Australia to explore the area with a team of international experts.

Branchiocerianthus is a giant hydroid that consists of a single polyp on a long stem living on a sandy bed. (SWNS)

Using the underwater robot SuBastian scientists are able to explore deep sea canyons and coral reefs that have never been seen before.

Schmidt Ocean Institute co-founder Wendy Schmidt said: “There is so much we don't know about the deep sea, and there are countless species never before seen.

“Our planet is deeply interconnected – what happens in the deep sea impacts life on land and vice versa. This research is vital to advance our understanding of that connection and the importance of protecting these fragile ecosystems.

“The Ningaloo Canyons are just one of many vast underwater wonders we are about to discover that can help us better understand our planet.”

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