Adult Keeled Millipedes have 19–21 body segments and some have lateral flanges or keels. They are eye-less and males have external, easily visible gonopods consisting of the modified first pair of legs of the seventh segment.
The Australian fauna consists of six families: Dalodesmidae, Pyrgodesmidae, Haplodesmidae, Opisotretidae, Polydesmidae and Paradoxosomatidae.