Saw 6-gill

Two bizarre new shark species discovered near Madagascar

These sharks certainly live up to their name.

Whether you’re fascinated or terrified by sharks, the list of species you need to consider has just grown by two. And they're pretty weird.

In the West Indian Ocean, marine scientists have discovered two new species of six-gilled sawsharks.

The new species — Pliotrema kajae and Pliotrema annae — join a third, previously discovered species of six-gilled sawshark, Pliotrema warreni.

These sharks are among the strangest, and most memorable, sea creatures we know of. Sawsharks are named for their saw-like snouts, which are lined with sharp teeth of varying size. In the middle of their deadly snouts, they have whisker-like barbels, which help them navigate the ocean and sniff out prey, including fish, crustaceans, and squid.

The “saw” comes in handy when it’s hunting time — the sharks use it to kill their prey by swiping side to side and cutting it up into bite-sized pieces.

The newly discovered species differ from other sawsharks, which usually have five gill slits on each side of their strange heads, not six.

That makes the new double discovery extra thrilling, lead author Simon Weigmann, a researcher at Elasmobranch Research Laboratory in Hamburg, says. Weigmann called the finding "simply astonishing."

"Astonishing" barely covers it; these sharks are pretty ridiculous looking, especially from below:
Researchers discovered two new species of six-gilled sawsharks.Simon Weigmann

Sawsharks live in the three major oceans — Pacific, Atlantic, and Indian — but are concentrated mostly in the western Pacific Ocean. The sharks can grow up to about 1.5 meters long.

"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."

Scientists' knowledge of these weird creatures is slim, the researchers say — the brand new pair of species underscore that fact. The sharks were found during a research mission to study small fisheries off the coasts of Madagascar and Zanzibar.

The findings were published Wednesday in a study in the journal PLOS ONE.

One of the new sawsharks, in all its weird glory.Simon Weigmann

Sawsharks under threat

One of the reasons why we’re still learning about these sharks is that they can swim deep in the water, out of human reach. But even as we are identifying new types of shark, they may also be declining in population.

Overfishing is likely to blame: “Considering their known depth distributions, both new species are likely affected by fishing operations,” Weigmann says.

One of the new shark species, Pliotrema annae, may be particularly vulnerable, because it has a smaller swimming range, is more rare, and lives in shallow waters (between 20 and 35 meters).

They've just been found, but knowing that these sharks are already under threat is a reminder of how important it is to study how fisheries affect different species, study co-author Andrew Temple, from Newcastle University, said in a statement.

"Last year our team highlighted the massive underreporting of sharks and rays caught in the South West Indian Ocean and the urgent need to expand efforts globally to assess the impact of these fisheries on vulnerable species," Temple said.

"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."

Abstract: Recent sampling efforts in Madagascar and Zanzibar, as well as examinations of six-gilled sawsharks in several museum collections provided evidence for a complex of species within Pliotrema warreni Regan. The present manuscript contains a redescription of P. warreni involving the syntypes and additional material, as well as formal descriptions of two new species of Pliotrema Regan. All specimens of both new species were found in the western Indian Ocean. Individuals of the first new species, hereafter referred to as P. kajae sp. nov., were identified originating from Madagascar and the Mascarene Ridge. Specimens of the second new species, hereafter referred to as P. annae sp. nov., were only found off Zanzibar. Pliotrema kajae sp. nov. appears to inhabit upper insular slopes and submarine ridges at depths of 214–320 m, P. annae sp. nov. so far is only known from shallow waters (20–35 m). Both new species differ from P. warreni in a number of characteristics including the known distribution range and fresh coloration. Taxonomical differences include barbels that are situated approximately half way from rostral tip to mouth, with prebarbel length equidistant from barbel origin to symphysis of the upper jaw in P. kajae sp. nov. and P. annae sp. nov. (vs. about two thirds way from rostral tip to mouth, with prebarbel length about twice the distance from barbel origin to symphysis of upper jaw in P. warreni) and rostra that are clearly and slightly constricted between barbel origin and nostrils, respectively (vs. rostrum not constricted). Pliotrema kajae sp. nov. differs from P. annae sp. nov. in a longer snout, more numerous large lateral rostral teeth and upper jaw tooth rows, jaw teeth with (vs. without) sharp basal folds, and coloration, particularly pale to light brown (vs. medium to dark brown) dorsal coloration with (vs. without) two indistinct yellowish stripes. A revised diagnosis of Pliotrema and a key to the species are provided.
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