Separation of two neotropical species Macrothrix superaculeata (Smirnov, 1982) versus M. elegans Sars, 1901 (Macrothricidae, Anomopoda, Cladocera)

The morphology of two Neotropical taxa, Macrothrix elegans Sars, 1901 and M. superaculeata (Smirnov, 1982) (Macrothricidae, Anomopoda, Cladocera) was redescribed, based on type materials (a lectotype of M. elegans was selected here), and additional samples from the Americas. Previous conclusion about synonymy of both species was erroneous, because it was based on limited material from South America. M. superaculeata differs from M. elegans in the presence of a sharp spine at postero-dorsal angle of valves; a more fine ring around dorsal head pore; thinner hexagonal reticulation of valves; the presence of setules on basal segment of postabdominal seta; armature of exopod on antenna II, and some features of thoracic limbs. Previously, the discriminative features of the two species were not formulated accurately, and it was a reason of several misidentifications. Actually, M. superaculeata is found only in a limited set of localities from the Amazon basin, while M. elegans is one of the most common anomopod species in all Neotropics, from Argentina to Mexico.