Populations of the Daphnia hyalina-galeata complex from Central, North and South Europe have been compared morphologically. The main purpose of this investigation is delimitation of the critical species Daphnia galeata, based on a thorough examination of the original materials from G. 0. Sars' collection, and taking into account hitherto overlooked or insufficiently appreciated characters. According to their morphology and ecology, Daphnia hyalina, Daphnia galeata and Daphnia cucullata have to be treated taxonomically as separate species. In view of the short and high antennula mound and other morphological characteristics, Daphnia gracilis Hellich and Daphnia hyalina lacustris sensu Lilljeborg belong to the species Daphnia galeata. In the common range of Daphnia galeata and Daphnia cacullata there occurs quite frequently an intermediary form, which according to genetic evidence is a hybrid of these two species. Although apparently this hybrid form is stabilized genetically to a large extent and is capable of identical reproduction, it should not be considered as a species in the usual sense.The present work intends to put the notoriously confused systematics of the Daphnia hyalina-galeata complex on a firm basis. It concludes with a key, which should enable also non-specialists to identify uniquely the three species and the hybrid form in question.
A new species of Neodiaptomus, N. intermedius n. sp. is described and illustrated. It is compared with related species of the strigilipes -physalipus species group.
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