Scientists say an ancient fossil found in China dubbed the "walking cactus" is not a plant but the first creature to walk on bendable, jointed legs.

Dating back about 520 million years, the fossilized thumb-sized, worm-like animal has been named Diania cactiformus in honor of its spiky look, ScienceDaily.com reported Thursday.

Jianni Liu of Northwest University in Xi'an, China, says the creature probably scurried along the bottom of shallow seas.

Its 10 pairs of long, sturdy legs surprised Liu when she first saw it, she says.

"I fell in love with this strange guy," she says. "Later when I observed it carefully under the microscope, I realized it was not only a funny one but an important one."

Its 10 legs appear to have carried a hard, outer covering of armor and joints that let them bend, features that would make the species the earliest known to have a hardened outer covering and also the first to have jointed legs, Liu says.

Today those features distinguish the arthropods, including crustaceans, insects and spiders.

"The significance of the find is that arthropods are, in terms of species, the most successful group on the planet," Liu says. "The secret of their success seems to be their legs."