Using genetic testing, the study confirmed that the new species, named the "Atlantic sixgill shark", is different than its counterparts in the Indian and Pacific Oceans.
"We showed that the sixgills in the Atlantic are actually very different from the ones in the Indian and Pacific Oceans on a molecular level, to the point where it is obvious that they're a different species even though they look very similar to the naked eye," said Toby Daly-Engel, Assistant Professor and shark biologist at the Florida Institute of Technology.
Measuring up to 6 feet in length, Atlantic sixgill sharks are far smaller than their Indo-Pacific relatives, which can grow to 15 feet or longer.
They have unique, saw-like lower teeth and six gill slits, as their name suggests, while most sharks have five gill slits.
With their new classification, Atlantic sixgill sharks will now have a better chance at long-term survival, Daly-Engel noted.
"Because we now know there are two unique species, we have a sense of the overall variation in populations of sixgills. We understand that if we overfish one of them, they will not replenish from elsewhere in the world," she said.
With ancestors dating back to over 250 million years, well before dinosaurs, sixgill sharks are among the oldest creatures on Earth.
Yet the fact that they reside at extreme ocean depths, sometimes thousands of feet below the surface, has made them especially challenging to study.
Using 1,310 base pairs of two mitochondrial genes, the team determined there are enough genetic differences between what had long been considered a single species, Hexanchus nakamurai, to rename the Atlantic variety Hexanchus vitulus.
Their findings were reported in the journal Marine Biodiversity.
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