Scientists have identified two new species of shark that live in the depths of the West Indian ocean.
The new species are six-gill sawsharks, which have distinctive snouts filled with teeth and catfish-like whiskers or feelers that help them detect prey.
One, Pliotrema annae, was discovered after being caught by fishermen in Zanzibar, while the snouts of the other species, known as Pliotrema kajae, were collected in Madagascar, with other specimens later found in museum collections.
Neither of the two shark species have been spotted alive in the wild.
"We were conducting shark and ray research with those fishers at the time and realized that these sawsharks did not match the existing species," said study author Andrew Temple, a research associate at Newcastle University in the UK.
"We have collected two so far - they are not common."
Temple said the discovery, published Wednesday in the journal PLOS One, showed "how important the western Indian Ocean is in terms of shark and ray biodiversity, but also how much we still don't know."
"The region is widely understudied, with the majority of what we know coming from work in fisheries. The difficulty is that small-scale fisheries dominate the region - with at least half a million fishers using 150,000+ vessels," he said via email.
"These fisheries are fairly spread out, with a relatively small number of vessels in each location. It makes monitoring them very difficult logistically, which has the knock-on effect of only seeing a small portion of the overall catches - which is why seemingly uncommon species like these might often go undiscovered for some time."
Prior to the latest discovery, there was only one known species of six-gilled sawshark.
"The six-gill sawsharks are really quite extraordinary as most sawsharks have five gill slits per side," said Simon Weigmann, a co-author of the study, who is based at the Elasmobranch Research Laboratory in Hamburg, Germany.
Sawsharks live on a diet of fish, crustaceans and squid, using their serrated snouts to kill their prey and, with quick side-to-side slashes, break them up into bite-sized chunks, said Temple.
They can reach up to about 1.5 meters (nearly 5 feet) in length and a bizarre, saw-like snout, with sharp teeth that alternate between large and small.
The other species, P. kajae, was identified after researchers combed through existing museum specimens, including two at London's Natural History Museum. After finding the snouts in Madagascar, they realized that some existing museum specimens had been mislabeled and were actually the newly discovered species.
Temple said that sharks were an incredible example of evolution and adaptation.
"They are so perfectly adapted to their environment and the world around them that they have existed, virtually unchanged, for millions of years," he said. "They were around before trees."