In the mountains of central Peru, the sloping forests are dotted by plots of coffee. Sections of old-growth trees are separated by row-filled coffee plantations and the homes of those who grow one of the nation's largest exports.

This region of the Andes belongs to the Pui Pui Protected Forest, an area established in 1985 and encompassing more than 148,000 acres, according to a study published Nov. 28 in the peer-reviewed journal ZooKeys.

Between 2012 and 2014, a research group led by Edgar Lehr, a professor of biology at Illinois Wesleyan University, conducted surveys of the creatures that call the protected area home, according to the study.

The team's work revealed seven new species of amphibians and three new species of lizards, researchers said.

Now, analysis of samples collected more than a decade ago has revealed there was another new species hidden in the findings.

Lehr's team collected specimens of frogs belonging to the Pristimantis genus, or robber frogs, according to the study. They were found at night along a mountain river on leaves just above the ground, researchers said.

This "cryptic" species was believed to belong to another species until DNA revealed it to be unique, researchers said.

Pristimantis vrazi, or Vráz's robber frog, was named after Czech explorer Enrique Stanko Vráz for his years spent exploring the region by boat and the collections he curated, according to the study.

"He published his travels and observations in South America in a book (published in 1900) that provides valuable original insights into South American nature and indigenous peoples at the end of the 19th century and still inspires people," researchers said.

The frog's back skin is "shagreen," a rough, leather-like appearance, while its throat and chest are "smooth," according to the study.

The coloration is marbled, with mottled gray, brown and cream colors, researchers said. On the end of the limbs, "finger and toe discs" are a "pale reddish brown" color.

The male frogs are smaller than the females, 0.5 inches and 1 inch respectively, common among hopping amphibians.

The hind limbs of all the frogs, however, are "long" and "slender" with rough skin and scattered bumps, according to the study.

The new species has only been found in two zones of the Pui Pui Protected forest, researchers said, and the samples were taken from the past surveys.

The research team recognized the large gap in time between the collection of frogs and the description of this new species.

"It is common practice for taxonomists to describe at first the 'easy' new species, those that are easily recognized based on unique characters, and leave the more challenging taxa for later," according to the study.

The Pui Pui Protected Forest is in the central Peru Andes, northeast from Lima.

The research team includes Lehr, Jiří Moravec, Yingtong Wang and Marek Uvizl.