A submersible research craft spotted the small, translucent octopus by chance around 2.5 miles (4 kilometers) underwater off Necker Island on the northwestern end of the Hawaiian Archipelago, the US National Oceanic and Atmospheric Administration (NOAA) said.
"As the ROV (remotely operated vehicle) was traversing a flat area of rock interspersed with sediment at 4,290 meters, it came across a remarkable little octopod sitting on a flat rock dusted with a light coat of sediment," the NOAA's Michael Vecchione said."The appearance of this animal was unlike any published records and was the deepest observation ever" for this type of marine creature, he added, in a statement released on March 2.
The octopus -- nicknamed "Casper the Friendly Ghost" on social media -- was caught on camera by the Okeanos Explorer, which the NOAA uses to explore underwater geology and marine life in little-known parts of the world's oceans.
Vecchione said the newly discovered octopus has a single row of suckers on each tentacle instead of the usual two, but is "particularly unusual because it lacked the pigment cells, called chromatophores, typical of most cephalopods, and it did not seem very muscular."
"It is almost certainly an undescribed species and may not belong to any described genus," he said.