An ethereal blue glimmer just below the waterline has lured scientists like wisps from folklore to three new glowing species of marine bristle worm (polychaetes).

Their genus name, Polycirrus, means 'many tendrils' in Latin. Looking at these otherworldly worms, you can immediately understand why.

Until now, we knew of only four species of Polycirrus with the ability to bioluminesce. In addition, there were only two species of Polycirrus described in Japan. This new discovery, led by marine worm expert Naoto Jimi, adds three new species to each tally.

Two of these worms have been named after supernatural entities from Japanese folklore, yokai. The third species' name pays tribute to former director of the Notojima Aquarium, Shinichi Ikeguchi, since this worm was found in waters near the aquarium, as well as off the Shirawara coast.

Polycirrus onibi, discovered in Notojima and Sugashima, is named after yokai not unlike the will-o-wisps of Western folklore. Onibi are spirits of the dead which appear as a floating ball of usually blue flame, and tend to inhabit damp areas in nature.

Ink painting depicting Japanese folklore spirit Onibi which appears as a floating ball of flame.
Illustration of an Onibi spirit. (Sekien Toriyama/Public Domain)

Polycirrus aoandon, found in Sugashima, is named after the yokai Aoandon, a ghost-like creature with blue skin, long hair, horns and sharp teeth, who wears a white kimono and carries a blue lantern. A sort of Bloody Mary figure, it's said Aoandon is invoked by those who've spent the night sharing supernatural stories.

Drawing of japanese folklore spirit Aoandon.
Artist Sekien Toriyama popularized the legend of Aoandon. (Public domain)

"The hazy violet-blue bioluminescence emitted by the Polycirrus species is strikingly similar to the descriptions of these creatures found in folklore," Jimi said.

This color of light has a relatively short wavelength, so it is absorbed less quickly by water than other colors and therefore travels farther underwater. That's why this kind of bioluminescence is usually associated with creatures of the deep. The color of these worms' glow is unusual, given their coastal habitats.

The worms were examined in the wild ocean, thoguh some specimens were also brought to the lab for further study.

Japan Underwater Films Corporation helped record the action. In the sea, researchers found the bubbles from the SCUBA gear could set off the worm's hypnotic light show. They saw similar results in the lab by nudging the worms' tentacles with tweezers.

Orange bumpy worm with yellow tentacles at one end.
P. ikeguchii is more orange than the other two species. (Naoto Jimi/Nagoya University)

The pattern in which these glimmering lights flickered was near identical in all three species.

When stimulated, the tentacles flashed for about 0.3 to 1.1 seconds, with each flash lasting about 0.15 seconds. The scientists also noticed that disturbing one area of tentacles didn't trigger flashing in neighboring tentacles, nor did the flashing synchronize in an individual.

The lights' intensity waned after about 30 seconds of stimulation, like a glow stick at the end of a rave. But after the worms were given a few minutes' break from scientific tickling, their bioluminescent response was able to recharge, returning to full brightness.

"The discovery that all three new species are luminescent has allowed us to link taxonomic and ecological findings and establish research that others can readily apply to the study of luminescent organisms," Jimi said.

The flashing lights might be a kind of warning system, to scare off predators, not unlike the motion-sensor security lights in our homes. Since these worms are known to spend a lot of time buried in mud, rock crevasses or the nooks and crannies of sponges, the researchers think this bioluminescence is used mostly for "emergency situations", when the worm's body is exposed. The fact that the scientists' poking, prodding and bubbling was the main trigger for the worms' bioluminescence in this study certainly supports this theory.

"Bioluminescence is a treasure trove of interesting and unusual chemistry," Jimi said.

"We intend to use our findings to deepen our understanding of the molecular nature of this phenomenon and apply this knowledge to the development of new life sciences technologies."

This study is published in Royal Society Open Science.