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Blind sea creature hunts with a light

The deep sea is a seriously dark place, so when a light shows up, even a tiny one, fish will swim up for a closer look. That seems to be the strategy behind the glowing red spots used by a relative of the jellyfish, called Erenna. Scientists have just discovered that these creatures have glowing red dots in their tentacles, which are probably used to lure fishy prey.

Erenna is a member of the group that includes corals and jellyfish. Its flickering red spots are surrounded by thousands of stinging cells that kill the fish when it gets too close.

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 the submersible vehicle Tiburon. The researchers decided the animals belonged to a new species that hadn't been described before.

Glow-in-the-dark colors are pretty common on marine animals, but they're usually blue or green, which can be seen over long distances under water. Red light doesn't travel far at all.

A few fish produce red fluorescent light, but Erenna (which doesn't even have eyes itself) is the first marine invertebrate known to produce red luminescence. This comes as a surprise because Erenna lives in the deep sea, and researchers have generally believed that animals in the deep sea couldn't even see red light.

Two of the three specimens had partly digested fish inside them. Fish are rare at the depths where Erenna lives, so Haddock's team believe that the red spots act as lures to attract the few fish that do swim by.

"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.

Many marine organisms produce bright blue or green light, but it's often used for defensive purposes. For example, some of Erenna's close relatives will shed their flashing parts when under attack. This distracts the predators while the prey make a quick getaway. Some reptiles shed their tails for similar purposes.

The new Erenna specimens are some of the only ones known to use glowing light for luring prey.

The researchers report their findings in the 8 July issue of the journal Science.