It's been 30 years since biologist Peter Ward saw a rare species of nautilus off the coast of Ndrova Island in Papua New Guinea.

In early August, he saw the species again during another trip to the South Pacific. Ward, a biology professor and researcher at the University of Washington, says he's one of only two scientists to have ever spotted the rare species, Allonautilus scrobiculatus.

"My colleague Bruce Saunders from Bryn Mawr College found Allonautilus first, and I saw them a few weeks later," Ward recalled in a recent press release, referring to the species' initial discovery in 1984.

Nautiluses are marine mollusks of the cephalopod family, distantly related to squid and cuttlefish. They're considered "living fossils," as their closely related predecessors can be traced back in the fossil record for 500 million years.

The creatures look as if a squid has taken up residence inside an enlarged shell. The elusive species of note is characterized by a slimy coating on its shell.

"It has this thick, hairy, slimy covering on its shell," Ward said. "When we first saw that, we were astounded."

"Some features of the nautilus -- like the shell giving it the 'living fossil' label -- may not have changed for a long time, but other parts have," Ward added.

The latest sighting came after Ward and his colleagues enticed the creature with "bait on a stick" -- fish and chicken on a pole descended between 500 and 1,300 feet below the surface.

Nautiluses are scavengers, and the free meal was welcomed by two nautilus species, the more common Nautilus pompilius and the rare Allonautilus scrobiculatus.

Researchers were able to capture specimens of each species and bring them to the surface to take tissue and mucous samples. Nautiluses can only tolerate a specific range of water temperatures, so they don't travel easily.

"They swim just above the bottom of wherever they are," said Ward. "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 2,600 feet deep is going to isolate them."

Their temperature preferences mean local populations become geographically isolated, leading to genetic and ecological distinctions.

This makes rare species especially vulnerable and difficult to protect. Ward says nautilus populations are declining as a result of fishing pressures.

"As it stands now, nautilus mining could cause nautiluses to go extinct," he said.