New York: An underwater research craft has spotted a "ghostlike" octopus that appears to belong to a previously unknown species.

The discovery on the ocean floor near Hawaii highlights how little is known about the deep sea, a United States zoologist said on Saturday.

The milky white creature, nicknamed "Casper the Friendly Ghost" by Twitter users, was caught on cameras mounted on the craft as it explored the Pacific Ocean at a depth of 4290 metres last week, the National Oceanic and Atmospheric Administration (NOAA) said.

Describing the animal as an incirrate octopod, one of two main groupings of octopods, NOAA said it was the first time an incirrate was spotted so deep in the ocean.