A critical review of the current taxonomy of the genus Daphnia O. F. Müller, 1785 (Anomopoda, Cladocera).

The genus Daphnia O. F. Müller, 1785 (Anomopoda, Cladocera) has become a model genus for ecological, toxicological, and evolutionary studies. At the same time, Daphnia is a well-known example of a genus with a confused taxonomy. This review aims to identify the main sources of confusion (natural and human-caused) for the current taxonomy of Daphnia. A complete check-list of all species-group names of Daphnia was built using the available literature sources. I graphed the total number of taxa and number of valid taxa described during each year, and estimated a curve of accumulation of formal taxa from year to year. Four main periods in the history of Daphnia taxonomy were recognized, with the latest decades showing an increased rate of valid taxa to more than 50%. Overall, only 24 % of 361 known taxa of species rank are valid. A failure to find real, sometimes fine-scale diagnostic characters, led to a tradition of pseudo-taxonomy based mainly on the body shape and other phenotypically plastic characters, e.g. associated with defensive structures. I recommend revising the suite of taxonomically informative characters by emphasizing the anatomical details of males and thoracic limbs of both males and females. Such a revision of global scale, should be conducted in close coordination with phylogenetic studies. But this revision is impossible without accurate redescriptions of all previously described taxa, and a continuous step-by-step resolving of taxonomic problems in each species group.