A University of Arizona entomologist's research into the leggiest creature ever found has landed him on National Geographic's list of the Ten Weirdest Science Stories of 2012.

Study of Illacme plenipes, a millipede with up to 750 legs, has become a significant sideline for Paul Marek, whose main area of study is luminescence in another, less leggy, millipede species.

Marek, a research associate in the UA Department of Entomology, rediscovered Illacme plenipes in 2005 in an oak forest in California. It had not been seen for 84 years before then.

"This millipede is something I think about a lot, even before I found it," Marek said.

"It is a mythical creature in the world of millipedes, and it was presumed to be extinct."

It was not. You just needed to turn over some big rocks to find it.

Marek and his brother took a trip to a "biodiversity hot spot" - an oak woodland just south of Silicon Valley, where some lush private land borders a new housing development. They turned over some 100-pound sandstone boulders and found the millipedes clinging to the undersides.

They're not easy to see, Marek said. About an inch long and less than a millimeter wide, the millipedes are the size of an errant button thread and can be easily mistaken for root hairs. "I just watch them to see if they move," he said.

Then he collects them and gives them a much closer look. As you might imagine, it's difficult to count all those legs on such a tiny creature.

Marek photographs them under a microscope and then affixes a digital dot to each segment on his computer.

He uses a mathematical formula to assign the number of legs to each segment.

The record, on one found nearly a century ago, is 750. Marek's leggiest specimen so far is a female with 666 legs.

These millipedes hold the record for legginess in the animal kingdom, and yes, these arthropods are members of the Kingdom Animalia.

Marek made three collecting trips to California, but limited his collection to 17 specimens.

These creatures are rare, and he suspects they are "paleo-endemic" - isolated in both geography and evolution. Their closest relatives (less leggy) live in South Africa, meaning the species separated more than 200 million years ago when the great land mass of Pangaea broke apart.

Marek announced his find in a publication in 2006, when he was at East Carolina University.

This year, he wrote a full taxonomy of the species for publication, including many details that earned it inclusion in the National Geographic "weird" list. The species is eyeless. It spins a silklike substance from thousands of hairlike appendages. Its mandibles are pinlike, and it has "rudimentary, less well-developed mouth parts."

There are a lot of questions Marek would like to answer about Illacme plenipes, such as the utility of its silk spinning and its method of feeding.

Marek says there are more millipedes waiting to be discovered. He recently discovered what he believes is a new species during an arthropod survey of the Santa Catalina Mountains.

Marek doesn't rule out one day finding a millipede that lives up to its name of "a thousand legs."

The average is about 100 legs, he said.

Contact reporter Tom Beal at tbeal@azstarnet.com or 573-4158.