Xystodesmidae

 ( Polydesmida ) 

Colors range from pitch black to pallid, often with vivid patterns. This family contains many colorful and distinctive species, including Apheloria virginiensis of the eastern U.S. and Harpaphe haydeniana of the western U.S. The Sierra luminous millipedes of the genus Motyxia exhibit the only known examples of bioluminescence in the Polydesmida. Species of Apheloria and Brachoria in the Appalachians exhibit Müllerian mimicry, in which unrelated species resemble one another where they co-occur.

This family also includes the cave-dwelling genus Devillea, notable for having more than the 20 segments (counting the collum as the first segment and the telson as the last) usually found the Polydesmida. For example, in the species D. tuberculata, adult females have 22 segments and adult males have 21, with a corresponding increase in the number of leg pairs (35 in adult females and 32 in adult males, excluding the gonopods). Some species in this genus also exhibit variation in segment number within the same sex, for example, in D. subterranea, adult males can have as few as 19 segments or as many as 23. The species D. doderoi has the maximum number of segments recorded in this family (29, including the telson).