The leggiest animal known on Earth With up to 750 legs, the millipede Illacme plenipes Cook and Loomis, 1928 (see photos) is the leggiest animal known on Earth. According to Marek, Shear and Bond (2012), who provided a recent, detailed redescription of the species (http://www.pensoft.net/journals/zookeys/article/3831/abstract/ ) in the periodical Zookeys, it is endemic to the northwestern foothills of the Gabilan Range in San Benito County, Silicon Valley, California. Illacme plenipes is only known from 3 localities in a 4.5 km 2 area. At present, two families are recognized in the order: Siphonophoridae and Siphonorhinidae. Among these families, three genera occur in the United States and Illacme is the only known Western Hemisphere representative of Siphonorhinidae. Illacme plenipes was described by O.F. Cook and H.F. Loomis in 1928 from seven individuals collected from a site located “a short distance after crossing the divide between Salinas and San Juan Bautista…in a small valley of a northern slope wooded with oaks, under a rather large stone”. In 2005 and 2007, new specimens were collected from near the type locality. Individuals of the species are strictly associated with large arkose sandstone boulders (see photo), and are extremely rare, with only 17 specimens known to exist in natural history collections . In contrast with its small size and unassuming outward appearance, the microanatomy of the species is strikingly complex (see photos). Based on functional morphology of related species, the extreme number of legs is hypothesized to be associated with a life spent burrowing deep underground, and clinging to the surface of sandstone boulders. .