Eerie undersea 'spaceship' turns out to be first glow-in-the-dark turtle

Researchers diving near the Solomon Islands have accidentally made a remarkable discovery: a glow-in-the-dark turtle.

Marine biologist and National Geographic explorer David Gruber was recently diving with a documentary team off the coast of the Solomon Islands when he encountered what he described as a "bright red-and-green spaceship".

It turned out to be something even more remarkable: a biofluorescent sea turtle, believed to be the first of its kind ever discovered.

Gruber's team said meeting the "super calm" turtle was "spectacular".

The glowing turtle was a hawksbill sea turtle, a species found in tropical oceans and listed as critically endangered. Only around 20,000 nesting females are thought to remain in the wild.

Related: The glow-in-the-dark animals dancing at 'nature's disco party'

The encounter raises a lot of questions about the rare species: why are they biofluorescent, and how do they use the ability to communicate with each other?

Gruber said that scientists have only started focusing on biofluorescence and bioluminescence — fancy terms for glow-in-the-dark creatures — in the last 10 years or so, but that since then the ability has been seen "everywhere" in the animal kingdom.

(For the record: biofluorescent creatures, like the hawksbill turtle, absorb external light and reflect it in a range of different colours; bioluminescent creatures create the light inside their bodies.)

Earlier in 2015, Gruber revealed the first footage of swell sharks using biofluorescence in the wild off the coast of California.