An expedition of scientists has recorded a mysterious family of orcas, known only through rumors and a few rare sightings.

The scientists spotted the elusive "Type D" orcas off of Cape Horn, Chile, in January.

The orcas may be “the largest undescribed animal left on the planet,” said expedition lead Bob Pitman, a researcher from NOAA Fisheries’ Southwest Fisheries Science Center, in a statement.

Type D orcas are easily distinguished from other killer whales by their much smaller white eye patches. They also have more rounded heads and pointier dorsal fins compared to Type A, B, and C orcas.

Breakdown of the orca types. Image: Albino.orca

All orcas are currently considered part of Orcinus orca, the largest species of the dolphin family. But genetic testing may reveal that Type D orcas are a new and different species.

The first known sighting of the animals occurred in 1955, when a pod of 17 Type D orcas stranded themselves on the shores of Paraparaumu, New Zealand.

It took another 50 years before the animals were captured on film, near a sub-Antarctic archipelago called the Crozet Islands. Pitman’s curiosity was piqued by those pictures, so he started fishing through thousands of orca images taken in the Southern Ocean.

In 2010, Pitman and his colleagues published a paper and six additional images of Type D orcas in the journal Polar Biology. “It is the most distinctive-looking form of killer whale that we know of, immediately recognizable by its extremely small white eye patch,” the study’s authors said. “Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S.”

Other researchers started to pursue the Type D orca. The conservation group Sea Shepherd filmed the first known video of a pod on their boat Bob Barker in 2014.

In addition to filming the animals, Pitman's expedition obtained three genetic samples of the orcas’ tissues by firing crossbow darts at them. This biopsy collection technique is common among whale researchers and is considered minimally invasive because the dart points make contact with blubber, not muscle.

“We are very excited about the genetic analyses to come,” Pitman said. “These samples hold the key to determining whether this form of killer whale represents a distinct species.”