First seen by government scientists in 1928, Illacme plenipes—"the acme of plentiful legs"—keeps such a low profile that for the rest of the 20th century the species was thought to be extinct. Then University of Arizona entomologist Paul Marek spied one near Silicon Valley.

Marek and colleagues' new paper—published Wednesday by the journal ZooKeys—offers the first scientific description of Illacme plenipes, including insights into its strange anatomy.

For one thing, females have up to 750 legs, and males have more than 550. Most other millipede species have between 80 and 100 legs apiece, Marek said. For another thing, Illacme plenipes can spin silk from long hairs that cover its back, thereby creating its own "clothing."

"It's the coolest millipede I've ever