Homology of the wing base sclerites in Ephemeroptera (Insecta: Pterygota) - a reply to Willkommen and Hörnschemeyer.

We revised the homology of wing base structure in Ephemeroptera (Insecta: Pterygota) proposed by Willkommen and Hörnschemeyer in a recent issue of Arthropod Structure and Development. The first free sclerite (s1) in Ephemeroptera should be homologized with a part of the first axillary sclerite (1Ax) of Neoptera, together with the second free sclerite, whereas the authors recognized s1 as a detached part of the anterior notal wing process. The fifth free sclerite of Ephemeroptera should be homologized with the median notal wing process of Neoptera, rather than it being homologous with a part of 1Ax in Neoptera, as the authors postulated. Hypothesized secondary fusion of the axillary sclerites in Ephemeroptera and Odonata proposed by the authors is premature, because the basal phylogeny of Pterygota is still poorly understood, and an alternative interpretation of morphological evolution (i.e., that undifferentiated axillary sclerites represent the ground plan of Pterygota) can also be drawn from the Ephemeroptera+Neoptera hypothesis.