4 (3) Dorsal setae absent from segments II to IV, or totally absent. Genitalia situated in 



segments V and VI NAIDIDAE (in part) 6 



4 (3) Dorsal setae present on all segments except the peristomium. Genitalia situated in 



segments X and XI TUBIFICIDAE (in part) 17 



5 (J) Worms exceed 1.5 to 2.0 mm in di- 

 ameter. Setae two per bundle on all 

 segments. Male pores situated on 

 segment XVIII. Citellum begins on 

 segment XIII MEGASCOLECI- 

 DAE 45 



Figure 5. — Generalized megascolecid ; lateral view, anterior segments. 



5 (3) Worms usually less than 1.0 mm in di- 

 ameter. Setae very rarely two per 

 bundle in every segment and may be 

 totally absent in some parts of the 

 body. Clitellum begins on segment XI 

 ENCHYTRAEIDAE 33 



Figure 6. — Generalized enchytraeid; lateral view, anterior segments. 



6 (i) Dorsal setae present, beginning in segment V. Ven- 

 tral setal bundle of segment II fan-shaped and di- 

 rected anteriorly Paranais litoralis 



Figure 7. — Lateral view, anterior segments. 



6 (4) Dorsal setae totally absent. Ventral setal bundle not fan-shaped 7 



^ 



(6) Worms commensal on gastropod molluscs, living in the mantle cavity and 



kidney. Setae with long strongly curved teeth (Fig. 8). .Chaetogaster limnaei 

 Figure 8. — Somatic seta. 



7 (C) Worms free-living. Setae with moderately curved distal ends (Fig. 9). 

 Figure 9. — Somatic seta. 



