The exact morphology of Oligoneuriella pallida (Hagen, 1855) from China (Ephemeroptera: Oligoneuriidae)

The brushlegged mayfly Oligoneuriella pallida (Hagen, 1855) has been reported from a series of countries by quite several different researchers, which also caused some confusions and inconsistence of morphological descriptions, and led to mis-identification of Chinese Oligoneuriella species historically. Here the Chinese oligoneuriid specimens are compared to European Oligoneuriella species morphologically and molecularly. The results show China harbors one species O. pallida. It can be diagnosed by nymphal long oval lamellae of gills I, fimbriate part of gill I longer than lamellae, subequal tarsi and tibiae of mid- and hindlegs, and all femora without hair-like setae on outer margins. In adults, the femora and abdomen of this species have grey to purple pigmented markings, well-developed titillators and subgenital plate. Remarkably, the Chinese O. pallida also shows some differences to European populations, like longer filamental part of gills I and spine-like setae on abdominal sterna of nymphs, and with pigments on femora and nearly straight posterior margin of subgenital plate in male adults. It has 6.15% K2P distance of COI gene to European sequence. The detailed description in the present study not only show the exact features of the species O. pallida but also provide good photos for further classification on Asian brushlegged mayflies, which is still lack of study and clarification.