The long-tailed river stingray or antenna ray, Plesiotrygon iwamae, is a species of freshwater stingray in the family Potamotrygonidae. It is found in the Amazon basin in South America.
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.
The species was described in 1987 by Hugo P. Castello from Museu de Zoologia, University of São Paulo. Previously misidentified, or unidentified, specimens were then found in other museums.
This fish seldom appears in the aquarium trade.