The image: A diver has discovered and photographed an eel unlike any other, living in an undersea cave near the isolated Pacific island nation of Palau. What has scientists buzzing is the fact that this eel apparently hasn't changed since it first appeared some 200 million years ago, around the dawn of the age of the dinosaurs. The "living fossil," known as Protoanguilla palau, has internal organs and body parts unlike those of any known eel, alive or extinct. As far as researchers know, it exists only in this cave 115 feet below the ocean's surface, although scientists speculate that its ideal habitat is more common in deeper water. Charles Darwin coined the term "living fossil" to describe animals that have survived for millions of years without evolving.

The reaction: This is remarkable, says Smithsonian Institution ichthyologist Dave Johnson, as quoted by Wired. The first eels in the fossil record appeared in the Cretaceous Period; this eel, with even more ancient features, "takes that back 100 million years earlier." P. palau "looks so bizarre — large head with relatively short body and various unique" internal characteristics — that scientists didn't think it was an eel at first, says researcher Masaki Miya in Discovery News. It has fewer vertebrae, fused skull bones, an upper jaw bone, and toothed gill rakers that initially baffled researchers. Now the challenge will be protecting this rare animal from collectors, who are "notorious for trying to keep every animal in their tanks."