Scientists have captured a “supergiant” crustacean in waters seven kilometres deep off New Zealand, measuring 10 times the normal size of related species.

The “supergiant amphipod”, which resembles a monster prawn, was found during an expedition to the Kermadec Trench north of New Zealand by scientists from the University of Aberdeen and Wellington’s NIWA marine research institute.

Amphipods are normally up to three centimetres long and the University of Aberdeen’s Alan Jamieson said he was stunned to find the 28-centimetre giant when emptying traps on his research vessel’s deck. Another amphipod, which was filmed by the expedition but not captured, was an estimated 34 centimetres long.

“It just goes to show that the more you look, the more you find,” NIWA principal scientist Ashley Rowden said. “For such a large and conspicuous animal to go unnoticed for so long is just testament to how little we know about life in New Zealand’s most deep and unique habitat.”

Supergiant amphiphods have been found only once before, in the 1980s. But that was off Hawaii and NIWA said it was yet to determine if the latest catch was a new species.