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Motyxia Chamberlin is comprised of eight species of bioluminescent xystocheirine millipede in which the gonopodal solenomere arisess at different positions, from basally and subbasally on the acropodite to being fused with the companion acropodal branch and detaching proximad or near midlength. Previous synonymies of Amplocheir Chamberlin and Luminodesmus Loomis and Davenport under Motyxia are confirmed as is its assignment to the tribe Xystocheirini, which is redefined. Component species are M. kerna Chamberlin, the type species, monica Chamberlin, sequoiae (Loomis and Davenport), tularea (Chamberlin), sequoia (Chamberlin), pior Chamberlin, porrecta Causey and Tiemann, and tiemannim Causey. Motyxia sequoia is comprised of two races, the nominate and sequoia alia Causey and Tiemann; sequoia ollae Causey and Tiemann is properly a subspecies of tularea. Motyxia pior form secca is an invalid name without standing in nomenclature, and M. tejona Chamberlin, and M. expansa and exilis, both by Loomis, are placed in synonmy under M. monica, the oldest name for the southernmost species, as Polydesmus dissectus Wood is referable to Xystocheir Cook the bioluminescence is a continuous, neon-white glow of the entire dorsal surface including the antennae and legs. Its visibility at night suggest a warning function analogous to aposematic coloration. The phenomenon may observe a circadian rhythm, and controlled photoperiod experimentation may be productive.