[3][4] Polyxenida differ from other millipedes in having a soft, non-calcified exoskeleton, unique tufts of bristles or setae, fewer legs (no more than 17 pairs), and an absence of copulatory appendages in males.

These distinctive barbed bristles can easily detach and become entangled in the limbs and mouth-parts of predatory insects, effectively immobilizing them.

[9][5] At least two species reproduce asexually by way of parthenogenesis, wherein females lay eggs without mating and males are absent or rare.

[3][10] For example, studies of the common species Polyxenus lagurus have found males scarce or absent in parts of northeastern Europe.

[11] Millipedes in this order grow and develop through a series of molts, adding segments and legs until they reach a fixed number in the adult stage, which is the same in a given species.

[17] Some authors place the extinct orders Arthropleurida and Eoarthropleurida (each represented by a single genus) within the Penicillata as a sister group to Polyxenida.