Two families worldwide, 1 in North America.
About a dozen species north of Mexico.
Body flat with tiny heads and 30 to 192 body rings. Eyes absent. Paranota always present. In males the 9th and 10th pairs of legs are modified as sex organs (gonopods). The usual color is pink. The rough dorsal surface has a narrow longitudinal groove. (1)
North America occurrence: southern West Virginia and central Kentucky to southern Alabama, Louisiana, and western Arkansas; Idaho; northern California (2)
Millipedes in order Polyzoniida lack paranota and a dorsal longitudinal groove, and are more round than flat.