Even within the quirky class of cephalopods, nautiluses are an outlier. These sole members of the Nautilaceae family, which first appeared 500 million years ago, are often called living fossils thanks to the fact that they haven't changed much in millions of years. There may have once been many different kinds of externally-shelled cephalopods populating the oceans, but these days, there are only seven known nautilus species—the rarest of which was just seen again for the first time in 30 years.

University of Washington biologist Peter Ward and a colleague discovered Allonautilus scrobiculatus off of Ndrova Island in Papua New Guinea in 1984. The species, which Ward described in 1997, was distinguished by significantly different gills, jaws, shell shape, and male genitalia as compared to other nautiluses. Additionally, it was covered in slime. "It reminds me of half a swimming ear muff," Ward told The Seattle Times. "It’s just a shaggy dog." Researchers had hoped that the distinguishing features would illuminate the long, slow process of nautilus evolution, but following that initial sighting, A. scrobiculatus effectively disappeared—until just recently.

Ward went back to study nautiluses in the South Pacific this summer. He and his colleagues baited the scavenging cephalopods by placing chicken or fish meat in cages, which they lowered 500 and 1300 feet below the surface and filmed for 12 hours at a time. One night, while reviewing the footage, Ward caught sight of the distinct slimy hair of an A. scrobiculatus. A second soon showed up, and the two jostled for the bait with the more common chambered nautilus before being overpowered by an 8-foot-long sunfish. But the important thing was that after 31 years, one of the rarest creatures on the planet had been spotted was again available for study.

Using the same baited traps, Ward's team was able to capture several A. scrobiculatus specimens, carefully bringing them to the surface and taking small tissue, shell, and mucous samples. Four of the animals were fitted with radio tags, after which they were all re-released.

It's the limitations presented by nautilus' natural habitats that create small but distinct populations that can evolve independently, as appears to have been the case with A. scrobiculatus. They can only exist within a very narrow depth range, creating isolated pockets of animals. "They swim just above the bottom of wherever they are," Ward told the University of Washington. "Just like submarines, they have ‘fail depths’ where they’ll die if they go too deep, and surface waters are so warm that they usually can’t go up there. Water about 2600 feet deep is going to isolate them."

This also means that as habitats are destroyed, entire species—like A. scrobiculatus—could be wiped out. "Once they’re gone from an area, they’re gone for good," Ward told the University of Washington.

To prevent this, especially in the face of rampant nautilus mining for their valuable shells, the U.S. Fish and Wildlife Service will discuss designating nautiluses as a protected species under the Convention on International Trade in Endangered Species of Wildlife Fauna and Flora next month.

[h/t io9]