A rare species of nautilus, Allonautilus scrobiculatus, was recently spotted in the South Pacific. But, it’s who saw it again that makes the sighting special.

“Before this, two humans had seen Allonautilus scrobiculatus,” said biologist Peter Ward. “My colleague Bruce Saunders from Bryn Mawr College found Allonautilus first, and I saw them a few weeks later.”

Until recently, the Allonautilus scrobiculatus hadn’t been seen in more than three decades. What are the odds that one of the first people to discover it would be the next person to see it again after a 31-year absence?

Nautiluses are often referred to as a “living fossil”

Nautiluses are smaller, distant cousins of squid and cuttlefish. It’s distinctive shell has given it the nickname of “living fossil.” These shells are seen in the fossil record going back an astounding 500 million years.

But, that doesn’t mean it hasn’t changed

A more in-depth look at Allonautilus scrobiculatus shows several areas of the animal stand out from other nautilus species. The gills, jaws, shell shape and male reproductive structures are noticeably different from other species.

“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,” said Ward.

Allonautilus’ shell is also covered in a “thicky, hairy, slimy covering,” according to Ward. “When we first saw that, we were astounded.”

How the Allonautilus scrobiculatus revealed itself after 31-years

Since 2011, Ward and his colleagues used “bait on a stick” systems to coax the scavengers out. Pieces of fish and chicken meat were suspended on a pole stretching between 500 and 1,300 feet below the surface. Then, the researchers waited as they filmed activity around the bait.

“This year, there were about 30 guys involved and each day we would all watch the movies from the night before at 8X speed. There were a lot of ‘ohs’ and ‘ahs’,” said Ward.

Then one night, Ward spotted what he was looking for.

Allonautilus and other nautilus

A rare Allonautilus scrobiculatus (right) swimming next to a Nautilus pompilius (left) off of Ndrova Island in Papua New Guinea. Credit: Peter Ward.

The pair of nautilus clashed over the bait until a sunfish showed up.

“For the next two hours, the sunfish just kept whacking them with its tail,” said Ward.

Ward and his fellow researchers also captured several nautiluses, including Allonautilus. They gathered small tissue, shell and mucous samples from them and were able to learn that most nautilus populations stick to themselves. This is due to the narrow range of ocean depth they are able to survive in.

“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.”

Because they are isolated like this, one species of nautilus is often genetically different from the other. This isolation also makes any conservation efforts a challenge. If one species dies from an area, they are usually gone for good according to Ward.

Ward is worried illegal fishing “could cause nautiluses to go extinct.”

What’s next for Ward and his colleagues? They want to see if they can find Allonautilus anywhere else. Right now, there located near Ndrova Island in Papua New Guinea.

Read Peter Ward’s fantastic National Geographic piece to learn more and for additional photos of Allonautilus.

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