Redescription of the Rio skate Rioraja agassizii (Rajiformes: Arhynchobatidae) with notes on internal anatomy and intraspecific variation

Abstract Rioraja agassizii belongs to the monotypic genus and differs from other Riorajini species of Atlantoraja by shape anterior nasal flap, squamation, clasper skeleton, body measurements color pattern. Although R. is a well-known species, commonly captured in inshore waters southwestern Atlantic, its external morphology internal anatomy have never been fully described little known on intraspecific variation within species. Juvenile adult, male female specimens were examined, measured dissected. Herein, we redescribe present detailed descriptions illustrations morphology, neurocranium, jaws, hyoid gill arches, pelvic fin girdle. Additionally, notes sexual dimorphism ontogenetic differences coloration, cranial measurements, dermal denticles are provided.