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Abstract
The larva, nymphal stages and adult of Hydrozetes longisetosus sp. nov. are described and illustrated, and the relationship of this species with the other European species of Hydrozetes is investigated. This species was first found at the edge of a forest lake, Dury 3, in the Tuchola Forest (Poland). Subsequently, we studied specimens that had been collected in 1976 by Dr H.M. Engelmann 40 km north of Görlitz Niederspree (Germany). Many adults of this species have three setae of the c‐series, which is rare in Hydrozetes and is considered a primitive character. Most adults have two pairs of p‐series setae, which is not common in Brachypylina and is unique among European Hydrozetes. The nymphal stages have many long setae in the marginal part of the gastronotum (whole l‐ and h‐series and seta p 1), and some or all long setae of the c‐ and d‐series, which is unique among European Hydrozetes. In H. longisetosus neotrichy occurs in the h‐series, as in H. parisiensis Grandjean, Citation1948. Therefore, the former species is closely related to the latter, and also to H. lacustris (Michael, 1882) and H. octosetosus Willmann, Citation1932, which rarely retain all the c‐series setae in the adults.
Acknowledgements
We are grateful to Prof. Dr Roy A. Norton, State University of New York, Syracuse, NY, USA, for the loan of the sample with H. longisetosus from Germany, for sending the sample with H. parisiensis, providing us with a copy of the Willmann (Citation1932b) paper, and for a thorough review of this manuscript and many valuable suggestions, and to M.Sc. Anna Nowicka, for collecting mites from lake Złocieniec.