The Spiny Butterfly Ray, Gymnura altavela, is found in tropical and temperate coastal waters with a discontinuous distribution: it occurs along the east coast of the United States of America, Brazil, and Uruguay in the western Atlantic Ocean, from Portugal to Angola in the eastern Atlantic, and also in the Mediterranean Sea. Globally, Gymnura altavela is considered endangered by the International Union for Conservation of Nature (IUCN). Our study analyzed the complete mitochondrial genome of G. altavela sequenced from an individual captured in the western Atlantic and compared it with a mitochondrial genome from a conspecific collected in the Mediterranean to explore if G. altavela comprises cryptic species. The newly assembled mitochondrial genome of G. altavela is 19,361bp in length and has 13 protein-coding genes (PCGs), two ribosomal RNA genes (12s ribosomal RNA and 16s ribosomal RNA), 22 transfer RNA (tRNA) genes, and a 3,659 bp control region. The gene order is identical to that reported for the specimen collected in the Mediterranean and that of the congeneric Long-tailed Butterfly Ray, G. poecilura. A phylomitogenomic analysis based on translated PCGs supported the monophyly of the genus Gymnura and indicated that genetic dissimilarity between G. altavela from the western Atlantic Ocean and the Mediterranean Sea was greater than that calculated among congeneric species belonging to the genera Mobula and Neotrygon, similar to that calculated among congeneric stingrays in the genus Hemitrygon, but lower than that calculated among congeneric species in the genera Pateobatis and Urogymnus. Overall, our comparisons suggest that G. altavela comprises cryptic species or at least indicates considerable genetic structure between populations in the western Atlantic and Mediterranean. We present these findings in a phylomitogenomic analysis of other Myliobatiformes and Rhinopristiformes. Additional phylogeographic and taxonomic studies of G. altavela are needed to support conservation efforts for this endangered ray that may comprise cryptic evolutionary units.