A tiny shark that secretes glow-in-the-dark fluid to conceal itself and catch prey has been identified as a new species.

In a study, a team of researchers revealed that the 5.5-inch specimen captured from the Gulf of Mexico in 2010 is an American Pocket Shark or Mollisquama mississippiensis. It is only the second pocket shark to be captured ever; the first pocket shark was observed in 1979 in the eastern Pacific Ocean.

"In the history of fisheries science, only two pocket sharks have ever been captured or reported," stated Mark Grace of the NMFS Mississippi Laboratories of NOAA and one of the authors of the study published in the journal Zootaxa. "Both are separate species, each from separate oceans. Both are exceedingly rare."

A Rare Catch

The study described five features of the American Pocket Shark that have never been observed in the original specimen found in the eastern Pacific Ocean. Both species, however, have two small pockets near each side of their gills that produce luminous fluid.

Grace and colleagues found the American Pocket Shark by chance during a survey onboard the NOAA ship Pisces in 2010. The team were studying sperm whale feeding in the Gulf of Mexico.

It was not until 2013, however, that scientists got a closer look at the mysterious creature. Grace teamed up with Michael Doosey of Tulane University Biodiversity Research, one of the authors of the study, to determine what species it was.

To identify the shark, the researchers photographed and analyzed internal and external features of the specimen. The most sophisticated images of the specimen came from the European Synchroton Radiation Facility in France, which provided x-rays that are "100 billion times brighter" than those used in hospitals.

Luminous Predator

Researchers explained that the shark uses the luminous fluid to hunt. While other species of sharks stalk and sniff out their food, the American Pocket Shark secretes luminous fluid that attracts its prey. The glow also completely obscures the predator, allowing it to pounce on an unsuspecting creature.

The American Pocket Shark is only the third species of sharks from over 500 that can secrete glow-in-the-dark liquid. The taillight shark has a similar gland on its tail.

"You have this tiny little bulbous luminescent shark cruising around in the world's oceans and we know nothing about them," said R. Dean Grubbs, a scientist from Florida State University who was not involved in the study, to the Associated Press. "It shows us how little we actually know."