A new species of tiny shark, which glows in the dark and squirts luminous liquid, has been discovered in the Gulf of Mexico. It is only the third of more than 500 known shark species, which is believed to secrete fluorescent liquid. It has been named the American pocket shark, Mollisquama mississippiensis, due to its diminutive size and because of the mysterious pocket-like pouches near its front fins, which it has been revealed are used to squirt little glowing clouds into the depths of the ocean.

The specimen — a 5.6-inch new born male shark — was collected during a 2010 survey to find out what Gulf of Mexico sperm whales eat. Scientists trawled in an area and at a depth where tagged whales had been feeding. National Oceanic and Atmospheric Administration ichthyologist (fish scientist) Mark Grace had spent three years identifying the collected specimens, and this one, still showing an umbilical scar, was in the last bag he opened.

The only other pocket shark known to science — a 16-inch adult female caught in the Pacific Ocean off Peru in 1979 — also has a pouch next to each front fin, which scientists were unable to determine the function for. But with this one, they realised what they did. The muscular glands are lined with pigmentcovered fluorescent projections, indicating they squirt luminous liquid, Grace and his collaborators wrote in the journal Zootaxa. The shark also has clusters of light-emitting cells dotted over its stomach.

The luminescence might conceal the shark from prey or from predators, he suggested.

A 2015 paper identified the shark as the second of its kind. It took years more, including high-resolution scans in the particle accelerator in Grenoble, France, to get more internal detail, to be sure it was a new species.