Davids, Kees, Sabatino, Antonio Di, Gerecke, Reinhard, Gledhill, Terence & Smit, Harry, 2005, On the taxonomy of water mites (Acari: Hydrachnidia) described from the Palaearctic, part 1: Hydrachnidae, Limnocharidae and Eylaidae, Zootaxa 1061, pp. 36-64: 36

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http://doi.org/ 10.5281/zenodo.170186

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Family Hydrachnidae 

The taxonomy of the species of this monotypic family, widespread and frequently found, in Europe has accumulated numerous unresolved questions. Many authors have paid too much attention to meticulous details in the shape of the frontal sclerite, and any species description based on such details promoted the "discovery" of additional presumptive taxa. Characteristically, many were found only once and never recorded again. The problems are enhanced due to the fact that in representatives of this family, preparation and slidemaking is particularly difficult, with the consequence that much museum material is in a bad state and important details cannot be studied in type specimens. Studies of intraspecific variability are urgently needed even for adults of the most common species. As taxonomically important characters can also be found at the larval stage, these investigations should ideally be accompanied by laboratory rearings and observations of larval morphology and behaviour, following the examples of Wainstein (1966, 1976) and Zawal (2003). Another necessary step is done here: revisionary work based on the available type material in order to clear the "taxonomic jungle" and to exclude from future work all those taxa which cannot be understood from bibliographical data and/or museum collections. As pointed out by Lundblad (1969) and Cook (1974), the system of Hydrachna  subgenera traditionally applied since K. Viets (1936) is highly artificial and not helpful for systemizing the diversity of the species of the genus. For this reason, we follow the viewpoint of K.O.Viets (1987) who proposed the synonymization of most former subgenera with the uniquely accepted genus Hydrachna  , and we add three further synonyms. Larvae of Microhydrachna Wainstein, 1976  , introduced as a separate genus, but also placed in Hydrachna  by K.O.Viets (1987), share characteristic morphological and behavioural distinctions that possibly justify the retention of this taxon as a subgenus. Further larval associations and investigations into larval characters are necessary in order to clarify this question.