Position of Moina wierzejskii Richard, 1895 (Crustacea: Cladocera) within the genus Moina Baird, 1850 in the light of new morphological data.

The family Moinidae (Crustacea: Cladocera) is intensively studied recently. Last genetic investigations revealed a huge diversity of species in the genus Moina Baird, 1850, comparable with the number of species in the genus Daphnia O.F. Müller, 1776. However, unlike daphniids, the taxonomy of moinids is understudied. Along with new still undescribed species, there are many inadequately described and illegitimately forgotten taxa within Moinidae. Moinids of tropical and subtropical regions remain especially poorly studied, and their features are ignored in recent intergeneric systems. Here we redescribe the morphology of M. wierzejskii Richard, 1895, a peculiar Moina from the New World, and discuss its position within the genus Moina s.l. In the taxonomic scheme, designed for European moinids, M. wierzejskii takes an intermediate position between subgenera Exomoina Hudec, 2010 and Moina s.str. Similarly to European species belonging to M. (Exomoina), females of M. wierzejskii have a modified Ilyocryptus-like labrum and an ephippium with two resting eggs. However, the males have no exopod on the thoracic limb I which suggests that this species is closer to the subgenus Moina s.str. The lack of exopod on male thoracic limb I was also marked in another species of the genus from the New World, M. hutchinsoni Brehm, 1937. To date such unusual combination of morphological features is unknown for any moinids from the Old World and Australia. We hope that our observations will stimulate deep phylogenetic studies of peculiar moinids inhabiting the New World.