[ref. ID; 6453 (Macro Ferraguti, Christer Erseus, Irina kaygorodova & Patrick Martin, 1999)]
Naididae and Lumbriculidae are freshwater taxa of oligochaete annelids, the former cosmopolitan in distribution and comprising about 175 species, the latter largely confined to the Northern hemisphere and with about 145 species. Both have traditionally been treated as separate families, although they have features in common with the larger family Tubificidae (bifid setae, atria and prostate glands associated with the male ducts). Recent phylogenetic studies using conventional morphological evidence have suggested that at least naidids are likely to represent apomorphic tubificids; they often have multiple setae of complex form as in freshwater tubificids and their genital organs are structurall of the same kind as in the tubificid subfamily Rhyacodrilinae (Erseus 1987, 1990; Brinkhurst 1994). Naididae differ from Tubificidae in the more forward location of these organs, a trait probably associated with the predominantly asexual mode of reproduction in the former. In oligochaetes with regular propagation by architomy, the position of genitalia is correlated with the number of segments regenerated at the anterior end (Hrabe 1937; Sperber 1948), and such genital shifts are prone to evolutionary shifts through cloning (Erseus 1984, 1990). Lumbriculidae also have atria and prostates similar to those of Rhyacodrilinae, but their basic gonadal sequence (see Brinkhurst & Nemec 1987 (ref. ID; 6423)), semi-prosoporous arrangment of the male pores (see Brinkhurst 1989), pair wise arrangment of somatic setae and lack of penial setae (see Brinkhust 1994) have been referred to as a support for the placement of lumbriculids outside the Tubificidae. On the other hand, there have been suggestions that Lumbriculidae are ancestral to Branchiobdellida, Acanthobdellida and the true leeches (Euhirudinea) (Sawyer 1986; Siddall & Burreson 1996), a view supported also by the phylgenetic tree presented by Brinkhurst (1994), who, however, finds this relationship improbable. The ultrastructure of spermatozoa has been used for assessment of family level relationships in oilgochaetes (Jamieson 1983, 1984, 1987; Jamieson et al. 1987).