M. alia M. bistipita M. kerna M. monica M. ollae M. pior M. porrecta M. sequoia M. sequoiae M. tiemanni M. tularea Amplocheir Chamberlin, 1949 Luminodesmus Loomis & Davenport, 1951 Motyxia is a genus of cyanide-producing millipedes (collectively known as Sierra luminous millipedes or motyxias[1]) that are endemic to the southern Sierra Nevada, Tehachapi, and Santa Monica mountain ranges of California.

Adult Motyxia reach 3 to 4 cm in length, 4.5 to 8 mm wide, with 20 body segments, excluding the head.

[2] The anterior 2–3 diplosegments are oriented cephalically (towards the head), a trait most distinct in M. sequoiae, nearly indistinct in Motyxia porrecta.

[7][8] However, the structure of the luminescent photoprotein remains uncertain, and its homology to molecules of closely related arthropods is unknown.

Besides Motyxia, the only known bioluminecscent millipedes are Paraspirobolus lucifugus (Spirobolellidae), from Japan and Taiwan, and Salpidobolus (Rhinocricidae), both in the order Spirobolida.

One study found Motyxia that glowed brighter also tended to have larger cyanide glands and were thus more toxic to predators.

While this implicates Motyxia's bioluminescence as an evolution for protection from predators, this study also notes that higher elevation millipedes glowed brighter.

Ultimately, the scientists of this study concluded that bioluminescence “may have initially evolved to cope with metabolic stress triggered by a hot, dry environment and was repurposed as a warning signal by species colonizing high-elevation habitats with greater predation risk.”[10] Another study provides further evidence for Motyxia's bioluminescence as a predator-deterrent.

[12] M. bistipita lives in low elevations of the Sierra Nevada mountains in California, in a hotter, drier climate than other Motyxia.

Individuals of the species M. sequoiae have been observed climbing on tree trunks, possibly consuming algae and lichens adhering to the bark.

[14] List of Species [15] The speciation of Motyxia is believed to have been driven by geological events and a drying climate following the most recent Pleistocene glaciation, while reproductive isolating mechanisms include rivers which are at their fullest levels in times when adults are most active, and marked differences in rainfall and suitable habitat across mountainous terrain.

[1] Within Xystodesmidae, Motyxia is placed in the tribe Xystocheirini along with the genera Anombrocheir, Parcipromus, Wamokia, and Xystocheir, all of which are native to California.

There is still a lot to learn about Motyxia's mating habits, their emergences into the night, and the exact evolutionary reasons for their bioluminescence.