Scientists believe they may have found a new species of octopus likened in appearance to Casper, the friendly cartoon ghost.

Researchers with the US National Oceanic and Atmospheric Administration made the discovery by chance as they searched the seabed on an unrelated mission collecting geological samples.

Teams were operating an unmanned submarine on the Pacific Ocean floor at depths of more than four kilometres (two-and-a-half miles) in the Hawaiian Islands when they spotted the unusual creature.

The Deep Discoverer submarine approaches the unknown octopod at 4,290 meters depth. Image courtesy of the NOAA Office of Ocean Exploration and Research, Hohonu Moana 2016. (NOAA)

One of the researchers, Michael Vecchione, said the camera was traversing a rocky plateau when it “came across a remarkable little octopod sitting on a flat rock dusted with a light coat of sediment”.

“The appearance of this animal was unlike any published records and was the deepest observation ever for this type of cephalopod”, he added, saying it did not have the normal shape and colouring associated with octopods found in deep water.

Mr Vecchione said the creature was believed to be a member of the incirrates suborder but had suckers in one, rather than two, series on each arm.

This ghostlike octopod is almost certainly an undescribed species and may not belong to any described genus, the NOAA Office of Ocean Exploration and Research said

“This animal was particularly unusual because it lacked the pigment cells, called chromatophores, typical of most cephalopods, and it did not seem very muscular,” he added.

“This resulted in a ghostlike appearance, leading to a comment on social media that it should be called Casper, like the friendly cartoon ghost. It is almost certainly an undescribed species and may not belong to any described genus.”