Demonstrating that the deep sea still holds mysteries, researchers at Scripps Institution of Oceanography have discovered transparent swimming worms that drop glowing “green bombs.”
The stranger-than-fiction worms were found in waters between 5,900 feet and 12,140 feet deep, mainly off the California coast. Measuring from 0.7 to 3.6 inches, the worms swim with clusters of bristles that act like paddles.
The discovery is reported in Friday’s issue of the journal Science.
Seven species were found by robotic vessels, five with the “green bombs,” as the researchers dubbed them.
Tiny spheres clustered near the worms’ front, the fluid-filled green bombs glow intensely for several seconds when released by the animals.
Researchers think these could be a defense for the worms, to distract predators. Similar “autotomy” (self-amputation) of bioluminescent structures has been found in a brittle star and a squid, according to the Science paper.
The worms’ closest relatives appear to belong to a group called acrocirrids, which usually live on the ocean floor, according to Scripps professor Greg Rouse, quoted in an institute news release.
Bioluminescence in sea life has medical applications. Last year, UCSD researcher Roger Tsien shared a Nobel Prize in chemistry for discovering what’s called “green fluorescent protein” in a jellyfish. The protein is now used by medical researchers as a tag on other proteins to track what’s happening in individual cells.
The green bombs appear to have evolved from gills possessed by the worms’ acrocirrid ancestors.
“The relatives have gills that appear to be in exactly the same place as the bombs,” Rouse said. “The gills can fall out very easily so there’s a similarity of being detachable, but for some reason the gills have been transformed to become these glowing little detachable spheres.”
The worms live at varying distances above the sea floor; four live close to the bottom, while the others live as much as 1,400 feet above the sea floor.
Moreover, these worms are not rare; two species have been found in densities as high as six per cubic meter, which is slightly larger than one cubic yard.
Rouse said the expedition’s success proved that there is far more to find in the ocean.
“The depths between 1,000 and 4,000 meters (3,280 and 13,120 feet) form the biggest habitat on Earth and also the least explored,” Rouse said. “With fairly limited time on submersible vehicles, mainly 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?”