The genus Pararhinebothroides was established for a species of cestode (Parahinebothroides hobergi) found parasitizing the Tumbes round stingray, Urobatis tumbesensis (McEachran & Chirichigno), in the inshore Pacific waters in the Gulf of Guayaquil, Ecuador. Its apparent affinities with the freshwater endemic genus Rhinebothroides were considered evidence to support the long-standing, yet controversial, biogeographical hypothesis that freshwater stingrays of the family Potamotrygonidae derived from a Pacific marine ancestor during the Cretaceous Period before the uplifting of the Andes. Here, we re-evaluate the phylogenetic and taxonomic status of P. hobergi based on examination of the available type material and newly collected material from the type host near the type locality. The new material allowed the description of tegumental structures using scanning electron microscopy and the generation of a hypothesis for the phylogenetic position of the species based on molecular data for the first time. Morphological investigations revealed that P. hobergi shares all the diagnostic features of the most recent concept of Anthocephalum, including the previously overlooked presence of bothridial apical suckers. Phylogenetic analyses based on partial 28S rDNA (D1–D3) and complete 18S rDNA sequence data for 4 specimens of P. hobergi, 45 species of other rhinebothriideans, and 5 non-rhinebothriidean outgroup species provided unequivocal support for the transfer of P. hobergi to Anthocephalum. Since this is the type and only species of the genus, Pararhinebothroides is considered a junior synonym of Anthocephalum, and Anthocephalum hobergi n. comb. is redescribed. Furthermore, our results reveal Rhinebothroides and Anthocephalum to be only distantly related among the Rhinebothriidea. Not only do our results confirm reservations expressed earlier about the affinities of P. hobergi, but they also substantially challenge inferences drawn previously about the biogeographical history of potamotrygonid stingrays based on parasitological data.

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