Changing Planet

See-Through Frogs With Green Bones Discovered in Peru

Centrolene charapita, one of four new frog species discovered in Peru. This species is semi-transparent. Photograph by Evan Tworney

Four new species of see-through frogs, three of which reveal green bones, have been discovered by researchers in northern Peru.

Showing their beating hearts and other body organs in x-ray detail, the newfound amphibians belong to the aptly named glass frog family (Centrolenidae).

Uncovered during extensive surveys in the Peruvian Andes, the “four remarkable species” were described August 12 in the journal Zootaxa.

The tiny frogs, which live alongside streams, include Centrolene charapita—named for a chili pepper that the yellow splotches on the back of this species resemble. Curiously, the two specimens that were collected had hind legs lined with fleshy, zigzag protuberances.

“We have no clue” why that is, acknowledged study co-author Santiago Castroviejo-Fisher, a herpetologist at Pontifícia Universidade Católica do Rio Grande do Sul in Brazil. Of the 150 known species of glass frogs, “less than ten have such ornamentation,” he said.

Fellow discoverer Evan Twomey, a frog researcher at East Carolina University in North Carolina, speculated that the leg frills could help to break up the frog’s outline and mask it from predators. “That’s a possibility, but it’s hard to know,” he said.

Gaudy Coloring

Cochranella guayasamini, which like many glass frogs is mostly green where it isn’t see-through, has distinctive yellow circles around the eyes. However, its tadpoles—which emerge from spawn laid on leaves overhanging mountain streams—are a vivid reddish pink before later turning green, according to the study.

The team said this gaudy coloring could be explained by a ramped-up system of blood vessels in the transparent tadpoles’ skin, which enable them to live in oxygen-poor sediments in the streambed.

But again, that’s only a guess: Glass frog tadpoles have barely been studied, and their natural history remains largely unknown, Twomey said.

A photo of the ventral side of a transparent frog, Chimerella corleone
A belly shot of Chimerella corleone, one of three transparent frog species discovered in Peru. Photograph by Evan Twomey

A third new species, Chimerella corleone, owes its mafia clan title to one team member’s obsession with The Godfather novel and film trilogy.

Detected only in the spray zone of waterfalls, the frog hardly looks menacing considering it’s just two centimeters (0.79 inches) in length. However, it does happen to conceal a spike-like bone in its upper arm, Twomey said.

“I guess it’s used for fighting between males,” he added. “So, for a frog that size at least, I’d say it’s fairly ruthless.”

C. corleone, along with the two species so far mentioned, were found to have green bones—a bizarre trait that’s actually widespread among glass frogs. The research team suspects the strange bone coloration is caused by an accumulation of a metabolic byproduct called biliverdin, a green bile pigment.

Green Bones Puzzle

Whether having green bones might in some way be advantageous to the frogs hasn’t been studied, Castroviejo-Fisher said, but “I have noticed that most frogs with green bones are arboreal [dwell in trees].”

A photo of a new species of transparent frog, Hyalinobatrachium anachoretus
Researchers found Hyalinobatrachium anachoretus residing much higher in the mountains than other species in this genus. Photograph by Evan Tworney

The fourth newly described species, Hyalinobatrachium anachoretus, was recorded in cloud forest at an altitude of 6,725 feet (2,050 meters). Other known species in this genus are found up to a maximum elevation of 3,280 feet (1,000 meters), so the find was “very unexpected,” Castroviejo-Fisher said.

The team discovered this frog in large numbers, but only on one particular night. Other nighttime surveys of the same area failed to turn up a single specimen.

The bigger mystery scientists are struggling to solve is why these and other glass frogs allow us to see straight though them. “Without a doubt, the adaptive, developmental, and genomic basis for the transparency of glass frogs is a long-standing question in zoology,” Castroviejo-Fisher said.

In the meantime, the backlog of undescribed glass frogs in South America is mounting. “We have a bunch of new species awaiting description in our offices,” Castroviejo-Fisher said.

The see-through frogs clearly have a lot more to reveal.


James Owen is a journalist and author based in Stockholm, Sweden. After cutting his teeth on the news and features desks of several UK newspapers, he struck out as a freelance writer, specializing in life sciences and natural history. His fish biography 'Trout' (Reaktion Books) was published in 2012.
  • Susan Newman

    What a fabulous discovery and they are so beautiful too!


    I think this species doesn’t exists before discovered 😉 joking ….. great discovery! !

  • Dwayne LaGrou

    Just imagine what we would look like if we were semi transparent. It would definitely put x-ray technicians out of work!!!
    Very cool Guys, Keep up the good work.

  • Vivian McAlexander

    Corleone glass frogs are amazing to learn about! Clear with green bones, and so cute. Frogs and toads are like something from science fiction, and they are well worth learning about if you love the strange and the unusual. Frogs that freeze solid then thaw out and are perfectly healthy?! Science fiction? Nope. This is a natural routine. The name of this frog escapes my mind at the moment, but do study frogs! They are like no other little critter on Earth. Have a little fun and relaxation while the world has gone utterly insane and cruel, and learn about frogs to escape for a little bit. “Ribbbbit!” – Vivian McAlexander (A nerd, and proud of it!)

  • bob

    so cool……………………………………………………………

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