The six-foot-long (two-meter-long) gelatinous animal was found floating dead off the Bahia coast by researchers from Brazil's TAMAR Program, a sea turtle conservation group.
Initial accounts quoted the scientists calling the creature "completely new, scientifically speaking."
But fish experts looking at video footage of the bizarre fish have identified it as a member of Ateleopodidae, a little-understood group of deep-sea fish known to science since the 1840s.
"As soon as I saw it, I knew what it was," said Dave Johnson, an ichthyologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.
The Brazilian team that had found the fish could not be reached for comment by press time.
Deep-Sea Jellynose Fish
Ateleopodidae—also called tadpole or jellynose fish—are known for their soft, blunt noses and scaleless, tapered bodies.
The fish have small teeth and are thought to be bottom-feeders, eating whatever they can suck off the seafloor.
About a dozen known jellynose fish species exist worldwide, Johnson said.
They can be found off the coasts of most major continents at depths ranging from about 1,300 to 2,300 feet (400 to 700 meters).
Jellynose fish can grow to more than six feet (two meters) long and, like many deep-sea fish, they have gelatinous bodies consisting of very little muscle.
"You don't ever see any hard, muscular fishes like tuna in the deep sea," Johnson said, since at those depths there aren't enough oxygen and nutrients to feed dense muscle tissue.
It's unclear whether the new Brazilian specimen belongs to a previously unidentified species of jellynose fish or if it's a species that's been found before, Johnson said.
"I don't think there's anybody in the world who could say by looking at that one specimen that it's an undescribed species," he said.
Complicating matters is the fact that scientists are not even sure how many jellynose species are already known.
That's because species are often described based on comparisons of similar specimens, and the jellynose specimens are in museums scattered around the world.
A comprehensive analysis of all those specimens will be necessary before scientists can clearly distinguish one species from another. So far, however, no one has volunteered for the task.
"They just haven't been well investigated," said marine biologist Jon Moore of Florida Atlantic University. "There isn't any commercial value to them, and they're rare [in the wild] and hard to get."
Moore has studied the diets of jellynose fish and agrees the newfound Brazilian creature is a member of the group.
But while the new specimen might not be a new species, it does set a new precedent for where the creatures are found, Moore said.
"I've never heard of anything [like this] caught off the Brazil coast at all," he said.