Three rare European “Alona” taxa (Branchiopoda: Cladocera: Chydoridae), with notes on distribution and taxonomy

Taxonomical efforts in freshwater zooplankton are continuously needed for the delineation of species. Even today, confusion exists in correct identification of several European Cladocera because of poor original descriptions and subtle differences in morphology. In this context, we discuss three of the rarest Alona-like Chydoridae in the Palaearctic and their validity. 1) Alona moniezi, only reported once from Vichy area, France, has a male indistinguishable from that of A. elegans Kurz, 1875 while females show characters of A. elegans and of Coronatella rectangula. We provide a description of this taxon, with intermediate morphology and discuss the possibilities of hybridization. 2) Alona karelica is unusual as one of the few eurythermic species of a predominantly stenothermic A. pulchella-group. We discuss Neotropical A. cf. karelica from Mexico as its closest relative. Both show similarities with the semi-terrestrial A. bromelicola from Nicaragua, forming a small A. karelica-section within the A. pulchella-group. 3) A. weltneri is redescribed based on type material and we confirm it as a member of the A. costata-group. We discuss the three taxa and expand their diagnosis. A. weltneri and A. karelica are both found sporadically, and little is known about their ecology. Their scarcity in the Palaearctic may be linked with specialisation to a peculiar habitat and the possibility that these are true relicts.