There is a new species of pocket shark roaming Earth’s oceans – and at 14 centimeters (5.5 inches) long, the shark certainly could fit in a pocket (a man’s pocket, that is).
The rare discovery was made in the waters of the Gulf of Mexico in 2010, splashed across headlines in 2015, and now carefully studied by a team of scientists. The shark, called Mollisquama mississippiensis (or American pocket shark), was collected by researchers aboard the NOAA ship Pisces during a trawl survey to explore fish and invertebrate prey linked with sperm whale groupings.
"If you can imagine how many fish have been trawled or fished from the sea, a number certainly in the billions, there has only been one of these captured and a single specimen of a related species," said study author Henry Bart, from Tulane University Biodiversity Research Institute, to IFLScience.
"Every time a new species is described it advances science, especially when novel scientific methods are used to describe the species, as was the case with the synchrotron imaging," added first author Mark Grace, of the NMFS Mississippi Laboratories of NOAA, to IFLScience.
The technology uses the world's most intense source of synchrotron-generated light to image in high resolution the internal anatomy of the pocket shark. It is located at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and produces X-rays that are 100 billion times brighter than those used in hospitals.
The pocket fish was collected 170 nautical miles south of the Mississippi River Delta. The other related specimen (M. parini) was found in 1984 in the Nazca Submarine Ridge of the Pacific Ocean. The two are notably different from each other: the American pocket shark exhibits a putative pit organ, two teeth differences, 10 fewer vertebrae than M. parini, six differences in body shape, and photophores that emit light irregularly across its body.
Photophores produce light through a chemical reaction but "with regards to the pocket shark, one can only speculate about the purpose for the photophores and there are a range of possibilities that include camouflaging, attracting prey or attracting mates, or a combination of options," said Grace.
"The reason that discoveries like this one haven’t happened before is that we know almost nothing about the biology of this species,” said Bart. “There has to be more of them out there; we just don’t know where to look."
The 2015 paper could not declare the creature a new species until further research as the differences could have been due to the sharks being different ages and sexes. The current identification, published in Zootaxa, was a partnership between Tulane and the NOAA Fisheries Service.
"The black color and photophores suggest it lives in the mesopelagic zone, a lightless zone between 200 and 1,000 meters depth. We don’t know much about any of the fish that live in this zone, but at least we have lots of specimens of other species of mesopelagic fish to study," added Bart.
"I think the most important thing about this discovery is that it emphasizes how little we know about the deep ocean. This little shark was caught at 580 meters or less. The deepest spot in the ocean is about 11,000 meters (deeper than Mount Everest is tall) and there are fish and other kinds of sea life down there that we know almost nothing about."