During the Hohonu Moana 2016: Exploring Deep Waters Off Hawaii expedition, while exploring at depths of over 4,000 meters (2.5 miles) northeast of Necker Island in the Hawaiian Archipelago, remotely operated vehicle Deep Discoverer encountered this octopod, dubbed "Casper" by the popular media because of its ghostlike appearance.
Not only was it unusual to see the octopus at this depth (the deepest published reports at the time for octopods lacking "fins" were all less than 4,000 meters), but it is almost certainly an undescribed species and may not belong to any described genus.
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Video courtesy of NOAA Ocean Exploration, 2016 Hohonu Moana.