Leggiest Animal Thrives Near Silicon Valley

Illacme plenipes, a Silicon Valley millipede, has up to 750 legs. Click to enlarge this image. Paul Marek
Paul Marek

Females of this newly found millipede get around on some 750 legs, while the males crawl about on 562 limbs.

The world's leggiest animal features up to 750 legs and may make its own silk "clothing."

The translucent species, Illacme plenipes, meaning "in highest fulfillment of feet," lives in the foggy, oak-forested outskirts of Silicon Valley, just south of San Francisco. Females of this millipede have a leg up over males, which possess a mere 562 limbs. That's still impressive, as most common garden millipedes have about 100 legs.

Paul Marek, a University of Arizona entomologist, told Discovery News that "all the legs evolved for burrowing in its deep subterranean habitat, and for clinging to the sandstone boulders."

Marek and colleagues also found that the ultra-leggy millipede possesses body hairs that produce silk.

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"We suggest that the silk may have evolved as a defense secretion or a means to keep their exoskeleton clean from parasites and little bits of junk that might accumulate on them in their subterranean habitat," Marek said.

This exoskeleton is jagged, scaly and translucent. He explained that many subterranean creatures, particularly those that live in caves, are de-pigmented and are translucent and/or white. It is energetically costly to produce pigment, and these animals do not need to maintain body coloration.

The millipede sports comparatively massive antennae that are used to feel its way through the dark because it lacks eyes. Its mouth, unlike other millipedes that chew with developed grinding mouthparts, is rudimentary. The scientists believe that its lower jaw swings down, allowing the sharp and pointy mandibles to pierce plant or fungal material.

"Once the plant/fungal material is pierced and exuding juices, the millipede sucks up the fluid through its tooth-lined labral opening," Marek said.

He continued, "Nearly all millipedes are decomposers and feed on decaying organic matter. They're an essential part of the ecosystem; they breakdown organic matter and release nutrients (like carbon, nitrogen and sugars) for future generations of life to use."

The closest presumed relative of the millipede is Nematozonium filum, which lives in South Africa. The common ancestor of N. filum and I. plenipes was able to spread to present-day California prior to the supercontinent of Pangaea breaking apart around 200 million years ago.

"Over millions of years, and through evolutionary time, the millipede became specially adapted to this unique area in California," Marek said. "It's known as a relict species because it is isolated both in space and evolutionary time. Because of this, and significant development (climate change, transit, housing and other human industry), the species is certainly in danger of further habitat loss and potentially extinction."

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The leggy animal's habitat is also home to other unique animals and plants, which include local flowers, trees, ferns, mosses, salamanders, scorpions, beetles and trapdoor spiders. Many of them are found no place else on Earth.

Casey Richart, a San Diego State University evolutionary biologist, agrees the leggy millipede "appears to be micro-endemic and should be of conservation concern. The importance of this species is potentially very high. Since it has diverged so anciently from its nearest relative, it likely has unique chemical compounds, some of which may have utility to human society."

Richart also wondered if the millipede could be the leggiest animal ever- past or present. As of now, no other known extinct or living animal has had more than 750 legs.

The millipede is described by Marek and colleagues, Jason Bond of Auburn University and William Shear of Hampden-Sydney College, in the latest issue of the journal ZooKeys.