Swimming worms cast green glowing bombs

By Beth Daley, Globe Staff

Scientists have discovered a group of deep sea worms that release bioluminescent spheres from their heads, possibly as a defense mechanism.

The ¾ to 3 1/2 inch worms – dubbed “green bombers” - live some 6,000 to 12,000 feet below the ocean surface and were discovered by scientists using remotely operated vehicles in the Pacific Ocean.

A transparent Swima worm with arrow pointing to one of its glowing "bombs" before release. (photo/Casey Dunn)

The researchers, led by Karen Osborn of Scripps Oceanography and including Laurence Madin of the Woods Hole Oceanographic Institution, found seven previously unknown species of the swimming worms. And fittingly, the group of transparent wrigglers was given the scientific name Swima bombiviridis. The findings were reported in the journal Science this week.

The researchers said the worms are common – but their living space is so hard to reach and observe that they were never seen before.

A video image of a species of Swima with arrows indicating the animal's large bombs. (photo/Monterey Bay Aquarium Research Institute)

“(This deep-sea region) form the biggest habitat on earth and also the least explored,’’ said Scripps Professor Greg Rouse, a coauthor of the paper and curator of Scripps Benthic Invertebrate Collection. “With fairly limited time on submersible vehicles, many off California, we’ve picked up seven new species. It goes to show that we have much more exploration ahead and who knows what else we’ll discover?”

Researchers weren’t able to see the worms release their glowing “bombs” in the wild since the submersible lights were so bright, but they witnessed it back on ships after the worms were caught. Five of the worm species have luminescent fluid-filled spheres that burst into light before fading after the animal releases them. The worms propel themselves with fans of long bristles that serve as swimming paddles.

Oddly, scientists say, the “bombs” appear to have once been gills that transformed over time into the spheres. The scientists found relatives of the worms that have gills that easily fall off in the same body location the “bombs” are found.