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Abstract
Based on SEM pictures the different evolutionary stages of shape and arrangement of microtrichia on the ventral side of the operculate gills (gill cover) in Caenidae are shown. There are a number of tendencies that can be observed in the evolution of these structures. The presence of different evolutionary stages of these structures in the Caeninae, Madecocercinae, and the newly postulated Clypeocaenis group is discussed and parallel developments in these taxa are assumed.
Acknowledgements
My special thanks go to Michel Sartori, Musée de Zoologie, Lausanne, Jan Peters, Florida A and M University, Tallahassee, Roland Grimm, Tübingen, Thomáš Soldán, Czech Academy of Sciences, České Budějovice and Arwin Provonsha, Purdue University, West Lafayette for leaving me the material for investigation. Thanks are also due to Arnold Staniczek and Susanne Leidenroth, both Staatliches Museum für Naturkunde, Stuttgart, for discussion, linguistic support, and help in making the SEMs.