The morphology of the articular region of the pectoral girdle and associated basals in Etmopteridae is revised in light of new evidence provided by taxa unavailable for previous studies. Such studies considered that etmopterids plesiomorphically had a single pectoral articular condyle, and only Etmopterus had two separate ones. Our reanalysis indicates that the possession of two separate condyles, one for the articulation of the propterygium and the second for the meso‐ and metapterygium, is the most widespread condition in this group. However, the presence of two separate articular condyles is not recovered as a synapomorphy for Etmopteridae. Previous studies also proposed that etmopterids lack a hook‐like process on the anteroproximal margin of the anteriormost pectoral basal. We document that the hook‐like process is plesiomorphically present in Etmopteridae, thus corroborating the hypothesis of closer relationships between this family and the other squaliforms that also share this process, namely Centrophoridae, Dalatiidae, Oxynotidae, and Somniosidae.

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Potamotrygon marquesi, sp. nov., is described and compared with other species of Potamotrygon occurring in the Amazon Basin. The identity of this new species is supported by an extensive external and internal morphological study including coloration pattern, squamation, skeleton and ventral lateral‐line canals. Morphometrics and meristics were used to further distinguish P. marquesi from congeners. Potamotrygon marquesi was first considered to fall within the range of variation found in P. motoro. However, even with an extensive variation in coloration observed in P. motoro, this new species presents a series of autapomorphies that confidently distinguishes it from what is understood as the morphological variation found in P. motoro. Additional morphological characters that diagnose P. marquesi include three angular cartilages, asymmetrical star‐shaped denticles, a single regular row of spines on tail dorsum, lateral row of caudal spines near the sting insertion, dorsal disc background in beige and grey mixed with shades of grey and bearing open and closed bicolored rings, among others. Although presenting a gap of distribution along the west–east extension of the Amazon Basin, its diagnostic charactistics are consistent in both recorded regions. Our study supports the need for many morphological characters to robustly distinguish members of Potamotrygoninae considering their extremely variable dorsal disc color pattern.

Agradeço primeiramente aos meus pais João Paulo Batista da Silva e Cacilda Capretz Batista da Silva, por seu amor, companheirismo, amizade e todo suporte necessário, imprescindíveis para realização deste trabalho. Agradeço também as minhas irmãs Nancy Capretz Batista da Silva e Juliana Capretz Batista da Silva por seu afeto e apoio em todas as etapas do meu trabalho. Ao meu orientador e amigo, Prof. Dr. Marcelo R. de Carvalho pelo conhecimento transmitido e por me ceder mais uma vez a oportunidade de trabalhar com um grupo tão intrigante de elasmobrânquios.