The Monterey Bay Aquarium Research Institute (MBARI) team, in California, were piloting a remote underwater vehicle in November when they spotted the underwater predator.
The arms can grow to more than 10m long.
“MBARI’s ROVs have logged thousands of dives, yet we have only seen this spectacular species nine times,” the Institute said.
MBARI said the giant phantom jelly was first collected in 1899, and had only been seen by scientists about 100 times since.
It has been found in ocean basins all over the world, except for the Arctic region.
“The challenges of accessing its deep-water habitat contribute to the relative scarcity of sightings for such a large and broadly distributed species,” MBARI said.
“Historically, scientists relied on trawl nets to study deep-sea animals.
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“These nets can be effective for studying hardy animals such as fishes, crustaceans, and squids, but jellies turn to gelatinous goo in trawl nets.”
Modern cameras and remote vehicles allow scientists to get a closer look than ever before at such deep-sea denizens.