When a team of explorers set out to look for the deepest shipwreck ever, the USS Johnston in the Philippine Sea, they ended up finding more than they expected.

About 6,200 metres below the water's surface, a young bigfin squid was spotted gliding along just above the sea floor.

Known for its long arms and tentacles, there have only been about a dozen confirmed sightings of the squid worldwide — and this was by far the deepest they've ever been seen.

"It was exciting for me," zoologist Mike Vecchione with Smithsonian Ocean told As It Happens host Carol Off. "I've been looking for cephalopods from these really ultra-deep environments for quite a long time."

Vecchione co-authored a study on the squid sighting with the chief scientist on the dive, Alan Jamieson, and they published their findings in the journal Marine Biology last month.

Once he received the footage and still images from the explorers, Vecchione said he could tell instantly from the outline of the creature that it was a bigfin squid.

"It's got a really big fin compared to the size of its body," he said. "But really, the most remarkable thing about it is, squids have eight arms plus two tentacles, which are modified arms. But in bigfin squids, the tentacles look very much like the other arms, and all 10 of these appendages have long, spaghetti-like extensions at the tips of them."

The squid captured on camera did not have those long extensions, which are more common in adults. That's why the zoologist believes it must have been a juvenile.

Previously, the deepest report of a bigfin squid was 4,700 metres below the Kermadec Trench in the Pacific Ocean. This young squid is roaming about a kilometre and a half deeper.

The discovery also means it's likely there are other creatures living nearby.

"Squid are important predators within the ecosystem that they belong in," Vecchione said. "There must be quite a bit of food in order to support these squids down there."

Though they exist kilometres below the water's surface, Vecchione also says he's concerned about the health of the ecosystems given the amount of pollution in the ocean.

"These ultra-deep environments of the trenches … they are a place where trash sort of gathers," he said. "That's been documented now in several of the trenches and actually, plastic has been found in the stomachs of some of the animals that live down there."

"I worry about the impact of that in terms of the entire ecosystem, since it's working its way through the food web."