A killer whale that could be a new species is to be studied by scientists for the first time after it was seen off the coast of southern Chile.

A team of international researchers have collected genetic samples from a group of orcas roaming the sub-Antarctic waters off the tip of South America.

For decades, fishermen and tourists had returned with tales and even photos of killer whales in the region that look distinctly different from others. But the enigmatic marine mammals had eluded scientists until now.

The team encountered the killer whales – known only as “Type D” – while anchored off Cape Horn for a week waiting for storms to pass in January.

Scientists collected three biopsy samples from the pod, and biologists from the US National Oceanic and Atmospheric Administration (NOAA) are now conducting laboratory tests that will establish if the orcas are a new species.

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“We are very excited about the genetic analyses to come,” said Bob Pitman, marine ecologist who was part of the team that spotted the whales.

“Type D killer whales could be the largest undescribed animal left on the planet and a clear indication of how little we know about life in our oceans.”

The unusual killer whales were first documented in 1955, when 17 of them were stranded on the coast of Paraparaumu, New Zealand. Compared to other killer whales, they had a more rounded head, a narrower and more pointed dorsal fins, and a tiny white eyepatch.

Initially, scientists speculated that the unique look might have been caused by a genetic aberration only seen in the stranded pod. But in 2005, a French scientist showed Mr Pitman photographs of odd-looking killer whales that had been poaching catches from commercial fishing lines near Crozet Island in the southern Indian Ocean. They had the same tiny eye patches and bulbous heads.

Unlike killer whale types A to C, they are thought to eat fish rather than marine mammals such as seals. They are also slightly smaller, at 20ft to 25ft long.

The whales are so different they probably cannot breed with other killer whales and are likely to be a new species, according to Mr Pitman.

An adult male ‘regular’ killer whale, top, and adult male Type D killer whale, bottom, with a smaller eye patch, more rounded head, and more narrow and pointed dorsal fin. (Uko Gorter/National Oceanic and Atmospheric Administration)

Some outside experts were more cautious. Michael McGowen, marine mammal curator at the Smithsonian Institution, said calling the whale a new species without genetic data was premature.

However, he added: “I think it’s pretty remarkable that there are still many things out there in the ocean like a huge killer whale that we don’t know about.”

The whales are hard to find because they live far south and away from shore "in the most inhospitable waters on the planet", said Mr Pitman.

"It's a good place to hide," he added.

The researchers followed the advice and directions of South American fishermen as they looked for the whales.

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After weeks of waiting, about 25 of the whales came up to the scientist's boat, looking like they expected to be fed.

Equipment problems prevented the scientists from recording enough of the whale songs, but they used a crossbow to get tiny tissue samples.

Mr Pitman said the whales are so big and their skin so tough that the arrow "is like a soda straw bouncing off a truck tyre" and does not hurt them.