The long-tailed river stingray or antenna ray, Plesiotrygon iwamae, is a species of freshwater stingray in the family Potamotrygonidae. Characteristic features are a long filiform tail, reduced eyes, and a low number of pectoral-fin radials. Their prey includes worms, crustaceans, mollusks, and small bottom fish (such as small catfish). They can detect electrical and chemical signals from prey in mud and sand. This fish seldom appears in the aquarium trade.