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"Pancake" Stingray
Photograph courtesy Zootaxa and Nathan Lovejoy, UTSC
This gallery is part of a special National Geographic News series on global water issues.
Resembling a pancake more than a fish, the freshwater stingrayHeliotrygon 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.
—Christine Dell'Amore
Published March 9, 2011
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Jaws
Photograph courtesy Marcelo Rodrigues de Carvalho
Like other freshwater stingrays, the disklike new fish species (pictured, H. gomesi's mouthparts) are likely ambush predators.
"Both of these guys, they sit on the bottom and wait for a fish to swim nearby," Lovejoy said. "When the fish comes near the front of the disk, [they] suddenly lift up the fronts of their disks like a garbage can lid."
The water—and fish—gets sucked underneath the stingray, allowing the stingray to "pounce" on its victim.
(See "Giant River Stingrays Found Near Thai City.")
Published March 9, 2011
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Stingless Stingray
Photograph courtesy Marcelo Rodrigues de Carvalho
The "little, degenerate" tail common to the two newfound stingray species can be seen in this picture of a young female H. gomesi.
Both new species are strange among stingrays, because they lack the large tail seen on most stingray species, which can cause painful injuries, said Lovejoy, who collaborated with the University of São Paolo's Marcelo Rodrigues de Carvalho on the study.
(See "'Crocodile Hunter' Death Extremely Rare, Caught on Film.")
"I’m not sure why that would be—it may be a deeper fish, [living] in habitats where it's not so worried about predators," he said. But "somehow it gets away without not having" a tail.
Published March 9, 2011
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X-rayed Ray
Image courtesy Ken Jones, UTSC
An x-ray of an H. gomesi reveals the hundred-plus strands of cartilage that extend out in all directions from the center of the stingray like beams of sunlight, giving the new genus its name—Heliotrygon is Greek for "sun stingray."
Although both new stingray species have been popular in the pet trade, they usually die quickly in captivity—mostly because they require massive quantities of live fish to eat, Lovejoy said.
(See pictures of freshwater plants and animals.)
Published March 9, 2011
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Primitive Eyes
Photograph by Oliver Lucanus
The new species' tiny eyes (pictured, H. gomesi) and pancake-like appearance make the stingrays more "plain looking" than other freshwater stingrays, Lovejoy said.
The smallness of the eyes suggests that the species inhabit dark, deep, and murky river areas, he added.
(Learn more about the Megafishes Project, an effort to document the world's biggest freshwater fish.)
Published March 9, 2011
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Latest But Not Last
Photograph courtesy Marcelo Rodrigues de Carvalho and Zootaxa
The new species (pictured, H. gomesi) represent the first new Amazon stingray genus since 1987—but it likely won't be the last, Lovejoy said.
"There are still big fish," he said, "that are waiting to be discovered."
(See pictures: "Nine Fish With 'Hands' Found to Be New Species.")
Published March 9, 2011
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