Description
These millipedes range from 4 mm to 30 mm in length. Colors range from pitch black through reddish or brownish to pallid and are rarely vivid. The collum is small, in the shape of a transverse oval, with a smooth anterior margin. The paranota are simple but usually well developed and dentate laterally. This family includes the notable species Polydesmus progressus, which exhibits sexual dimorphism in segment number: Whereas adult females of this species feature the 20 segments (counting the collum as the first segment and the telson as the last) usually observed on the order Polydesmida, the adult males feature only 19 segments.
