Platydesmida, Callipodida, Chordeumatida, Polyxenida, Stemmiulidae
Polyzoniidans have a somewhat domed dorsal surface with a flat ventral side. Their heads are small and cone-like, with few ocelli. They lack a dorsal groove and paranota (lateral extensions of each segment).
The order Polyzoniida contains three families:
The family Hirudisomatidae occurs from Spain to the Himalayas in Eurasia, Japan, and in North America from southwest Canada to central Mexico.
Polyzoniidae has a holoractic (northern hemisphere) distribution, occurring in the northwest and northeast United States, eastern Canada, and in Europe from the United Kingdom and France to Siberia.
Siphonotidae has a southern distribution, occurring in Brazil and Chile, South Africa, Southeast Asia, Indonesia, Tasmania, and New Zealand.