Sharks don't always bring up the best image to our minds, but this newly (re)discovered shark may change that perception.
Named the 'pocket shark,' it spans 5.5 inches long and is a touch smaller than an American dollar banknote, and it's also bioluminescent.
A pocket-sized glow-in-the-dark shark. It's enough to make you go 'aww.'
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The pocket shark
The reason this shark is able to glow in the dark is due to having glands that produce bioluminescent fluid, in a little pocket right behind its pectoral fins. Hence its name.
Adding to that, it also has light-producing organs called photophores dotted all over its body.
The pocket shark was first discovered back in 1979 off the Chilean coast, but it then didn't reappear until 2010 in the central Gulf of Mexico. And no one knows the reasons why it hasn't been spotted since, or in between 1979 and 2010.
Only now has it been classified as a new species, and so far only two pocket sharks have ever been spotted. As Mark Grace, a biologist at the National Oceanic and Atmospheric Administration (NOAA) said, "In the history of fisheries science, only two pocket sharks have ever been captured or reported."
"Both are separate species, each from separate oceans. Both are exceedingly rare," he continued.
Hotly anticipated and next up at #AES15: Mark Grace on the pocket shark! Squee! pic.twitter.com/IVc5IKw6yp— Shark Advocates (@SharkAdvocates) July 16, 2015
Another question that comes to mind is if only two pocket sharks have ever been seen; then, where are all the others?
This is a perfect example of how little we know about our oceans. There has been a lot of ocean discovery and research, but much still largely remains unknown.
A #shark with a pocket? @NOAA biologist Mark Grace explains at @NMNH 2-4PM #WorldOceansDayhttp://t.co/1Vw4XZg9sUpic.twitter.com/YjI27lbZ1c— NOAA Fisheries (@NOAAFisheries) June 8, 2015
"The fact that only one pocket shark has ever been reported from the Gulf of Mexico, and that it is a new species, underscores how little we know about the Gulf - especially its deeper waters - and how many additional species from these waters await discovery," said Henry Bart, the director of the Tulane Biodiversity Research Institute.
Bioluminescence in fish
This certainly isn't the first species of underwater creatures to boast glow-in-the-dark features. According to NOAA, around 90 percent of species living in open water have bioluminescent functions.
Bioluminescent uses differ, some work to attract potential mates, others as snares to entrap their prey, and some to warn off toothy predators.
According to the Smithsonian National Museum of Natural History, an animal's glow is triggered by a chemical reaction that emits light energy.
Both species of pocket shark have this bioluminous fluid, but aside from that, little else is known about these little swimmers.
The research was published in Zootaxa.