Abstract
Members of the family Siphonorhinidae Cook, 1895 are thread-like eyeless millipedes that possess an astounding number of legs, including one individual with 750. Due to their cryptic lifestyle, rarity in natural history collections, and sporadic study over the last century, the family has an unclear phylogenetic placement, and intrafamilial relationships remain unknown. Here we report the discovery of a second species of Illacme, a millipede genus notable for possessing the greatest number of legs of any known animal on the planet. Illacme tobini sp. n. is described from a single male collected in a cave in Sequoia National Park, California, USA. After 90 years since the description of Illacme, the species represents a second of the genus in California. Siphonorhinidae now includes Illacme Cook & Loomis, 1928 (two species, USA), Kleruchus Attems, 1938 (one species, Vietnam), Nematozonium Verhoeff, 1939 (one species, South Africa) and Siphonorhinus Pocock, 1894 (eight species, India, Indonesia, Madagascar, Vietnam).
Highlights
The genus Illacme is the sole representative of the Siphonorhinidae in the Western Hemisphere
Live millipedes were collected by hand, or in some cases lifted with a paintbrush or forceps if necessary
For comparison with I. tobini sp. n., we examined the 17 known specimens of I. plenipes from the Smithsonian Institution (USNM), Florida State Collection of Arthropods (FSCA), Virginia Museum of Natural History (VMNH), and Virginia Tech Insect Collection (VTEC)
Summary
The genus Illacme is the sole representative of the Siphonorhinidae in the Western Hemisphere. The family Siphonorhinidae has yet to be sampled by recent phylogenomic estimations of the class Diplopoda (Brewer and Bond 2013, Fernandez et al 2015) Illacme species and their colobognathan relatives exhibit true anamorphosis (euanamorphosis), whereby six-legged hatchlings develop into adulthood in coordination with the addition of new segments (Enghoff et al 1993). The microhabitats of siphonophoridan species are usually within deep substrata and individuals are frequently discovered beneath large stones (e.g., I. plenipes in California) and embedded inside large decaying logs (e.g., Siphonophora species in Central America) Persistence in these microhabitats is consistent with their morphology, including a lack of eyes, depigmented exoskeleton, shortened legs, and an elongate flexible body. The Siphonophorida in Arizona and California are found in relatively mesic oak woodlands in mountain foothills, including those of the Coast Ranges (CA), Sierra Nevada (CA), and Madrean Sky Islands (AZ)
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