Two New Zealand snorkelers were mystified when coming across a bizarre, all-black, two-legged fish on a white seafloor in a bay near Auckland.

So James Beuvink, 20, and his girlfriend, Claudia Howse, 19, scooped up the specimen and put it into the boat's livewell where it started slowly walking around, GrindTV reports quoting Fairfax Media.

"It had these little legs … I'd never seen anything like it," Beuvink told Fairfax Media. "It was pretty chilled out. It's not the biggest fish I've ever caught, but it was certainly the strangest."

They eventually sent the fish to the Museum of New Zealand Te Papa Tongarewa in Wellington, New Zealand, where collection manager Andrew Stewart examined it and put photos of it on Facebook, where it started gaining world-wide attention.

In an email to GrindTV, Stewart identified the specimen as a striped anglerfish, also popularly known as a striped frogfish.

"The last time this species was sent to us was 2008, which gives you an idea of how 'rare' they are here," Stewart wrote. "Elsewhere, the striped anglerfish is very common especially in the tropical and subtropical waters from the Atlantic, Indian and Pacific Oceans.

"The Frogfishes family (Antennariidae) are rare in our waters and seem to be at their southern limits of tolerance, water temperature-wise. They are taken as single captures, and have only been found along the east coast of the northern North Island."

What struck Stewart as "very unusual" was the fact this striped frogfish was completely black. They are often brightly colored.

"This is the first time I've seen one jet-black, with no body markings at all," Stewart told Fairfax Media.

"This particular species is strongly striped, and those stripes extend inside the mouth. So even when it's sneaking up and its mouth is open, its prey just doesn't get an inkling of what's about to happen to it."

That's because of the incredible speed at which it can catch prey, GrindTV reports.

"Frogfishes have the fastest bite of any vertebrate," the Museum of New Zealand Te Papa Tongarewa wrote on its Facebook page. "Their mouths expand at the speed approaching a .22 rifle bullet — and that's in a medium 800x denser than air."

The lure on its dorsal fin is used to attract smaller fish, which won't know what hit them when the frogfish decides to strike. It opens its mouth, swallows its prey and closes its mouth again all in six milliseconds.