Neuromast distribution and its relevance to feeding in Neotropical freshwater stingrays (Elasmobranchii: Potamotrygonidae)

The mechanosensory system in batoids has a unique sensory canal distribution located on both dorsal and ventral surfaces of the body. Due to the opposite position of eyes and mouth, ventral lateral-line canals are essential to detect and capture prey buried in the substrate. The present study analyzes the density of neuromasts in ventral lateral-line canals as well as their specific distribution patterns to help to understand the mechanisms involved in the foraging activities in potamotrygonid stingrays. The organization of the lateral-line canals was described in Potamotrygon albimaculata, P. jabuti and P. schroederi. Neuromasts were quantified in each canal of the ventral surface and endemic their densities were compared among P. albimaculata, P. jabuti, P. schroederi, P. wallacei, and Paratrygon aiereba. The orbito-nasal component of the infraorbital canal was examined for all genera of Potamotrygoninae to understand its origin and connection patterns. Despite similarities in the morphology of the lateral line in the examined potamotrygonid species, differences of the densities of neuromasts were observed. The distinct web-like infraorbital canal in Paratrygon aiereba held a significantly higher number of neuromasts, which apparently compensates the lower density of neuromasts along its ventral surface. The orbito-nasal component of the infraorbital canal presents connections between infraorbital and nasal canals, except for P. aiereba, which has a supra-infraorbital canals' connection. The complex distribution of lateral line canals and their neuromasts indicate distinct sensory abilities that probably provide a high capability to detect a variety of prey in different types of substrate.