For 33 years, Peter A. Rona has pursued an ancient, elusive animal, repeatedly plunging down more than two miles to the muddy seabed of the North Atlantic to search out, and if possible, pry loose his quarry.

Like Ahab, he has failed time and again. Despite access to the world's best equipment for deep exploration, he has always come back empty-handed, the creature eluding his grip.

The animal is no white whale. And Dr. Rona is no unhinged Captain Ahab, but rather a distinguished oceanographer at Rutgers University. And he has now succeeded in making an intellectual splash with a new research report, written with a team of a dozen colleagues.

They have gathered enough evidence to prove that his scientific prey - an organism a bit larger than a poker chip - represents one of the world's oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature itself, known from fossils, was once thought to have gone extinct some 50 million years ago.

Has the long pursuit frustrated him? "No," Dr. Rona replied as he displayed traces of the animal in sedimentary rocks some 50 million years old. "It's science. It's detective work. It's about racking up one clue after another."

Still, in an interview at Rutgers, Dr. Rona said he looked forward to eventually capturing one of the creatures alive. "I think it's likely," he said, "if we can do the dives." Dr. Rona, an authority on the deep sea, likes nothing better than to cram himself into a tiny submersible and fall into the abyss.

It takes more than two hours to descend to the creature's abode, which lies more than two miles down. The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change. For instance, sea lilies, marine animals with feathery arms, date back more than 400 million years.

Dr. Rona has found that P. nodosum thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided patterns that look curiously like the hearts of Chinese checkers boards. He has photographed thousands of the hexagons and found that large ones have 200 or 300 holes.

Dr. Rona's inability to catch the creature itself means that even though scientists have given it the fossil's name, they still vigorously debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.

Other deep sea sleuths who share Dr. Rona's fascination with P. nodosum can be found at Yale and the Woods Hole Oceanographic Institution on Cape Cod, as well as institutions in France, Canada and the United Kingdom.

"He's got the drive of curiosity," said Adolf Seilacher, a paleontologist at Yale and co-author of the new paper who first contacted Dr. Rona three decades ago to discuss the creature. "Real scientists, naturalists, are extremely curious."

Dr. Seilacher added that P. nodosum was a most unusual animal, especially because the many holes at the surface of its abode link up below in a labyrinth of subsurface tunnels.

"It's not just any fossil but a demonstration of a very complex way of life," he said in an interview. "It's a building plan, a behavior that makes this animal erect this gallery system. It's a lifestyle that is very, very old."

Dr. Seilacher said the earliest forms of Paleodictyon dated to the explosion of complex life in the Cambrian period some 500 million years ago. The animals began existence in shallow waters, he added, and gradually expanded into the dark habitats of the deep sea.

Dr. Rona became fascinated by the abyss in a roundabout way. His first love was rocks and mountains. In 1957, he received a master's degree in geology from Yale and went to work for Standard Oil, exploring the American Southwest for promising sites.

But in 1958, while visiting his family in Manhattan over the Christmas holidays, he came upon groups of oceanographers and research ships, their vessels moored to West Side piers. The famous scientists, in New York for a meeting, spoke of a vast new world.

By the early 1970s, armed with a doctorate in marine geology and geophysics from Yale, Dr. Rona was exploring the deep Atlantic for the National Oceanographic and Atmospheric Administration. He used dredges, cameras and echo sounders that mapped the seabed.

In 1976, he stumbled on the living fossil.

Dr. Rona and his colleagues were towing a giant camera sled, its strobe lights firing every few seconds, lighting up the seabed and recording the images on big reels of 35-millimeter film. Weeks later, back in his Florida office, Dr. Rona examined the freshly developed film.

His head began to spin.

What were all the holes? And what made the patterns?

At first, Dr. Rona assumed the film developers were pulling a prank. Then, as a magnifying glass drove home the reality of the holes, he got paranoid and weighed the possibility that the patterns represented the footprints of alien creatures from outer space that were colonizing the remote seabed. Fortunately, he let that idea drop, and began interviewing the best marine biologists he could find, first in Florida, then in Washington at the Smithsonian Institution. He struck out. No one had a clue.

In 1978, Dr. Rona and a colleague, George F. Merrill, published a paper that ruled out many possibilities and called the mystery animals "invertebrates of uncertain identity."

The breakthrough came soon thereafter. Dr. Seilacher, then at the Institute of Geology and Paleontology at the University of Tübingen, in Germany, wrote Dr. Rona to say the organism bore "perfect identity" with the fossil P. nodosum. He called the link "beyond any doubt."

In his letter, Dr. Seilacher suggested that the two scientists collaborate to study the creature. "I would love to participate in this adventure," he wrote.

Nothing happened. The Atlantic site was too remote, too costly to scrutinize.

In 1985, all that changed. Nearby, Dr. Rona and his colleagues discovered a riot of hot springs and bizarre life, including millions of shrimp. Suddenly, governments around the globe found the wherewithal to send oceanographers racing to the middle of the North Atlantic to explore the teeming springs.

Dr. Rona's creatures lay less than a mile way. Piggybacking on high-priority missions, he managed to visit the muddy site repeatedly, making submersible dives in 1990, 1991, 1993, 2001 and 2003. On the latter dive, he and Dr. Seilacher went down together.

Their collaboration made them improbable movie stars. In 2003, IMAX released Volcanoes of the Deep Sea, featuring their hunt for the living fossil.

Repeatedly, Dr. Rona tried to capture living specimens. He would have a hollow plastic tube lowered over a hexagonal spot and scoop up a thick core of seabed mud. But detailed inspections of the muck never revealed anything of significance - no body parts, no biological fibers, no DNA.

The 2003 dive of Dr. Rona and Dr. Seilacher did, however, produce hard evidence that finally linked the animal to P. nodosum. The robot arm of the submersible Alvin directed a hose that squirted water at a hexagonal array of holes, slowly removing layers of mud. The delicate operation quickly revealed a hexagonal array of subsurface tunnels identical to those of the fossil.

"For me," Dr. Rona recalled, "it was a eureka moment."

In May, the team's new paper appeared in the online version of Deep-Sea Research, Part II, an oceanographic journal published twice monthly. The printed article is due out in September.

The paper - more than a dozen pages filled with dense type, figures and photographs - reviews the evidence of more than three decades and concludes that the hexagonal forms "are identical" with P. nodosum, backing the conclusion Dr. Seilacher reached long ago.

The paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Dr. Seilacher, who backs the burrow idea, sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat.

Dr. Rona sees the holes as body parts, perhaps from a type of compressed sponge. The lack of biological clues, he said in the interview, may arise because microbial predators eat the remains after the creatures die.

The reason the team had captured no living specimens, he added, may lie in the great age and number of empty abodes, or bodies. Dr. Rona said the area's light sedimentation meant fresh-looking holes "can persist on the seafloor for hundreds of years."

Neither man will give in to the other on the subject of what the holes represent - despite their collaboration of more than three decades.

"Disagreement is necessary in science," Dr. Seilacher said. "It's good because it forces you to find new arguments and more arguments."

Dr. Rona seems eager to find new evidence and arguments. He talks excitedly of new dives to the inky world of Paleodictyon as well as the possibility of setting up a remote camera on the seabed that would try to catch a glimpse of the ancient survivor as it grows and interacts with its dark environment.

"It's an exceptional window into the past," he said of the creature. "Now we need to solve the mystery of what it is. We need to recover a specimen."