Ref ID : 5855
Michael Dzwillo; Phylogenetic and taxonomic problems in freshwater Oligochaeta with special emphasis on chitinous structures in Tubificinae. Hydrobiologia 115:19-23, 1984
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Setae and chitinous penis sheaths are the main characters used to distinguish genera and species of the subfamily Tubificinae. Genital setae and penis sheaths are of functional importance to facilitate copulation. Similar structures in different genera may be homologous or products of parallel evolution (homoiologous). Form and dimensions of the penis sheaths of many tubificine species are very variable. Transspecific overlap of quantitative species characters can make the determination of specimens in the genus Limnodrilus difficult. The configuration of the distal ends of the penis sheaths is an important character to distinguish Limnodrilus species. The definition of the intraspecific variability of this morphological character is problematic.