Ontogeny as a way to understand morphology of nasal capsule structures in Pipidae, with focus on Pipa arrabali (Lissamphibia: Anura)

After more than one-hundred years of studies, there is still no consensus regarding the names for the nasal elements in Pipidae and their correspondence to that of other frogs. Names vary depending on authors' preferences for an explanatory process associated with the observed state of the structure. Some of the names indicate absence, while others indicate fusion. As naming morphological structures relates to some sort of consensus regarding systematics' knowledge, one would expect results of the two activities to go hand-in-hand. Within the monophyletic Pipidae, one would expect that the names of structures would be all settled. However, the situation is the contrary. Our efforts to pursue such a research and properly name the involved structures resulted in a deeper understanding of the evolution within the taxa involved. Herein we present the results of the study of embryos and juveniles of P. arrabali; based on which we offer additional evidence for the proper naming of the involved elements of the nasal region. Furthermore, using key structures as topographical markers, and by comparing our evaluation to those presented by previous researchers, we have sorted out the compound nature of some key structures and present a proper naming for the morphology investigated.