Revisão taxonômica e morfológica de Potamotrygon signata Garman

Abstract

The order Myliobatiformes comprises the rays with a caudal serrated sting and includes the only subfamily completely adapted to the freshwater environment: Potamotrigoninae, endemic to South America and characterized by the reduction of osmoregulatory structures related to the marine environment present in other elasmobranchs. This subfamily is divided into four genera comprising 38 valid species. Nonetheless, the delimitation of the species has several problems, which can compromise the identification process due to the large intraspecific variation, mainly in relation to the color of the disc, one of the main characteristics employed for the identification of the species. Potamotrygon signata is found in the Northeast region of Brazil and is endemic to the Parnaíba River basin. Although some aspects of its morphology, and even feeding behavior, have already been studied, there is a lack of more indepth morphological studies with this species. Consequently, the present study intends to redescribe the species in detail, based on its morphology, in order to precisely redefine its taxonomic limits. For this purpose, the ventral and dorsal disc coloring patterns were analyzed, as well as the morphology of structures such as dermal denticles and the organization and arrangement of spines in the tail dorsal. Measurements were also taken in order to verify morphometric proportions that could help in the specific delimitation of P. signata. The skeleton was analyzed using radiographed or cleared and stained material, as well as through dissections. Finally, illustrations were made in order to document the morphological characters analyzed. The present study presents the first description of the ventral lateral line canals of Potamotrygon signata, in addition to expanding its morphological knowledge, reinforcing its high intraspecific variation.