1 Proandric (male funnels in 10). Holoic, with V-shaped nephridial bladders. Variably sized, from small to large (60–500 mm). Segment number 80–450.. Proandricus
– Holandric or metandric (male funnels in 10 and 11, or only in 11).......................2
2 Holandric or metandric (male funnels in 10 and 11, or only in 11); dorsal blood vessel simple throughout the whole body length; excretory system holoic with J-shaped nephridial bladders. Medium-sized (60–250 mm). Segment number 180–450................................................................................................................... Kazimierzus
– Holandric (male funnels in 10 and 11); dorsal blood vessel double in certain preclitellar segments, simple when crossing septa; excretory system holoic, with large or medium-sized, tightly coiled loops and elongated, V-shaped nephridial bladders..................................................................................................................................3
3 Coiled nephridial loops bushy, very large, V-shaped nephridial bladders widely open. Spermathecae always located posterior to testis, multiple in all or in some of the segments. Very large (550–2600 mm). Segment number usually over 500, may exceed 1200...................................................................................... Microchaetus
– Small, bushy loops of holoic nephridia, with V-shaped nephridial bladders. Spermathecae located anterior or posterior to testis, or in testicular segments. Mature individuals small or medium-sized, not reaching 500 mm, with the segment number between 100 and 500................................................................................ Geogenia