July 7, 2005—Many deep-sea creatures use blue or green luminescent light to defend themselves, but this relative of the jellyfish has twitching appendages that glow red—apparently to lure fish to their death.

Steven Haddock of the Monterey Bay Aquarium Research Institute and his colleagues collected three Erenna specimens off the coast of California during a deep-sea dive in a submersible. The animals, which cannot themselves see, belong to a new species of siphonophores, the group that includes jellyfish and corals. They are the first marine invertebrates known to produce red luminescent light, and they're all the more surprising because researchers have generally believed that deep-sea animals can't detect red light.

The flickering red spots, seen close up in the bottom photo, are surrounded by thousands of stinging cells that kill fish that get too close. Two of the Erenna specimens had fish inside them. The scientists propose in tomorrow's issue of the journal Science that the light-emitting appendages are lures to attract rare fish and that perhaps the ability to see red light is more common in the deep sea than previously thought.

"Some deep-sea fish have sort of night vision goggles. We're proposing that these fish are looking for red. If one comes close and sees this bright red twitching thing, that would really catch its attention," said Haddock's coauthor, Casey Dunn of Yale University.

—David Braun