Apparently it is an amphipod:
From the depths of the Kermadec Trench, New Zealand scientists have retrieved the largest known examples of a creature that looks like a giant albino flea.
On a recent research trip to the trench to determine how far down fish could be found, staff from Niwa and the University of Aberdeen found “supergiant” amphipods – deep-sea scavengers that feed on dead material.
“When the first big trap came out, first of all we said, great, we’ve got five fish,” Niwa’s Ashley Rowden said.
“But then we looked and said, `What the hell is that?”‘
Not only were the amphipods a record size – the biggest was just over 28 centimetres – but they were found seven kilometres below the ocean’s surface, far deeper than before.
Deep-sea amphipods, a relation of the sandhoppers that can be found on any beach, are typically two or three centimetres long. The research team knew of only two occasions when “supergiants” had been found anywhere in the world, with the last Kermadec sightings in the 1950s.