Two New Wonderfully Weird Species Of Six-Gilled Sawshark Have Been Discovered

The three known species of sixgill sawshark. The two new species flank the original known species. From left to right: Pliotrema kajae, Pliotrema warreni, and Pliotrema annae. Simon Weigmann

They might not be the most handsome bunch in the seas, but this line up of chainsaw-faced critters includes two brand new species of super-rare sawshark. 

The newly discovered Pliotrema kajae and Pliotrema annae, nicknamed by the researchers as Kaja's and Anna's six-gill sawsharks, were discovered by looking at specimens found in local fisheries on the coasts of Madagascar and Zanzibar.

Off the back of specimens and evidence gathered from East Africa, the team then compared the sawsharks to specimens found in a number of museums across the world. Using anatomical measurements, high-resolution photographs, and scanning electron microscope imagery, the team was able to confirm there was clear evidence of two species that had never been scientifically documented before. 

"The six-gill sawsharks are really quite extraordinary as most sawsharks have five-gill slits per side,” lead author Dr Simon Weigmann from the Elasmobranch Research Laboratory in Hamburg, said in a statement

"So it was really exciting to find a new six-gill sawshark species and to find two new species – well, that was simply astonishing!"

Sawsharks are an order of sharks that are made up of two genera: Pliotrema and Pristiophorus. Before this discovery, there was only one known species of the six-gill sawshark in the genus Pliotrema. Now, thanks to this new project, it has two more members. 

The sharks are officially described in the open-access journal PLOS ONE.

Pliotrema kajae, typically found in subtropical waters of the western Indian Ocean. Simon Weigmann,

Sawsharks – not to be confused with sawfish – can reach up to about 1.5 meters (just under 5 feet) and are known for their saw-shaped snoots used to hunt fish, crustaceans, and squid. They look especially bizarre from beneath, either cartoonishly like someone who has accidentally snapped a selfie with their smartphone’s front camera, or that they're judging you and found you wanting. However, their eyes are actually found on the top of the head, perfect for gazing upwards as they stalk around the shallow coastal waters looking for prey. 

The researchers say their new discoveries highlight how little we know about the biodiversity of coastal waters around the world. Rather worryingly, it also shows researchers and experts are unaware of how vulnerable these poorly managed fisheries and ecosystems may truly be.

"The discovery re-enforces both how important the western Indian Ocean is in terms of shark and ray biodiversity, but also how much we still don't know,” Dr Andrew Temple, study co-author from Newcastle University in the UK.

"Knowledge of sawsharks in the western Indian Ocean is generally still scarce. But considering their known depth distributions, both new species are likely affected by fishing operations,” added Dr Weigmann.

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