This gallery is part of a special National Geographic News series on global water issues.
Resembling a pancake more than a fish, the freshwater stingray Heliotrygon rosai (pictured) is one of two new species identified in the Amazon, a new study says.
H. rosai and Heliotrygon gomesi have been sold in the global pet trade for years under trade names. But only recently did scientists—working with local fishers from the Nanay River near Iquitos, Peru (see map)—gather enough specimens to declare the stingrays new species, said study co-author Nathan Lovejoy.
What's more, the fish are so distinct they constitute a whole new genus, the animal-classification level above "species," the study says.
(See a giant freshwater stingray caught in Asia.)
Growing up to 1.6 feet (0.5 meter) long, the stingrays may be relics of a time when ocean water and wildlife inundated parts of South America tens of millions of years ago—a phenomenon supported by geological and fossil data, said Lovejoy, an ecologist at the University of Toronto Scarborough.
When the saltwater retreated, some marine species stayed, evolving into new freshwater forms. Today these animals live in an area of diverse river ecosystems that Lovejoy calls the "Great Barrier Reef" of South America.
The new stingray species study was published February 24 in the journal Zootaxa.