SCIENCE LAB SPECIAL. : OCEAN VOYAGES

Most corals are immobile and build sprawling reefs. This one can walk.

Corals come in an array of shapes, sizes and colors, and they build sprawling reefs that serve as refuges for vast amounts of biodiversity in the ocean. But they are not known for being fleet of foot.

This is because out of more than 6,000 species of coral known to science, most are colonial organisms -individual animals that make their homes next to and on top of one another.

And as adults, these corals are immobile.

But there's another kind of coral that's completely solitary. And some of these animals, known as mushroom corals, can walk.

'' They're very little,'' said Brett Lewis, a marine ecologist in Australia. '' And they're adorable.''

Using time-lapse cameras and an aquarium that blocked out all other light, Dr. Lewis put inch-long mushroom corals through an experiment. One side of the aquarium had a sliver of white light ; the other had a small beam of blue light, like you would find in slightly deeper areas of the ocean.

In each of three trials, the mushroom corals showed a strong preference for the blue light, inching their way toward it, Dr. Lewis reported.

The research shows that the mechanics of the corals' movement are surprisingly similar to the way one of its closest cousins, the jellyfish, gets around.

The World Students Society thanks Jason Bittel.