Class Oligochaeta Grube, 1850 - oligochaetes see [unranked] oligochaetous Clitellata
   Subclass Tubificata Jamieson, 1988
     Order Tubificida
       1 Family Tubificidae Vejdovský, 1876 - sludge worms see Family Naididae Ehrenberg, 1828
       2 Family Enchytraeidae Vejdovský, 1879
       3 Family Capilloventridae
       4 Family Phreodrilidae
       5 Family Dorydrilidae
       6 Family Opisthocystidae see Family Opistocystidae Černosvitov, 1936