In the depths of the Pacific Ocean, newly discovered species of free-swimming worms have a unique method of distracting predators. They deploy "bombs" that burst in a flare of green light.

The annelid worms, which live between 1800 and 3800 metres below the waves, have been discovered by a team led by Karen Osborn of the Scripps Institute of Oceanography in San Diego, California. "I first got interested because these were not like any worms I had ever seen before," said Osborn.

The worms have elliptically shaped organs at their front end, about 1 to 2 millimetres in size. When captured worms were examined in the lab, Osborn noticed the organs being ejected into the water, where they started shining brightly for several seconds before slowly dying away.

Bioluminescence is common in the deep sea and is used by creatures for a range of purposes, including avoiding predators, communication and attracting prey. Osborn thinks her worms use their glow bombs to distract predators while they make an escape.

"It's really exciting to have found this whole unknown group, and it shows that there is so much we have still to learn," she says.

Journal reference: Science, DOI: link