From the streambeds in the Western Ghats of India, an international team of scientists has unearthed a species of tadpole that burrows through sand and lives in total darkness until they fully develop into froglets.

The tadpole of the Indian Dancing Frog family, Micrixalidae, was the only family of frogs and toads for which the tadpoles remained a mystery.

They were discovered and documented by a group of scientists from the University of Delhi, University of Peradeniya in Sri Lanka, and Gettysburg College in US. 

"We provide the first confirmed report of the tadpoles of Indian Dancing Frog family. These tadpoles probably remained unnoticed all these years because of their fossorial nature, which in itself is a rare occurrence in the amphibian world," said S.D. Biju, professor at the University of Delhi.

Genetically identified as Micrixalus herrei, these tadpoles are endowed with muscular eel-like bodies with extensive tail musculature that aids them in underground movements.

The findings, published in the journal PLOS ONE, showed that these tadpoles inhabit interstitial spaces within sand and make gravel beds of forest streams, starting from very early to late tadpole stages. 

Their eyes are covered with skin, which facilitates burrowing through gravel beds as well as provide them protection from abrasion. 

They lack teeth but have well-serrated jaw sheaths, which may help prevent large sand grains from entering the mouth while feeding and moving through sand. 

Their gut contains small sand grains together with decaying organic matter, which acts as a nutrient source.

Presence of lime sacs or endolymphatic sacs was also found in these tadpoles, which acts as a source of calcium carbonate for tadpoles and juveniles.

The Indian Dancing Frogs were also found to typically wave their legs as a territorial and sexual display while sitting on boulders in streams. 

The study reiterates the uniqueness of amphibians of the Western Ghats biodiversity hotspot, providing a platform for future studies on this amphibian family, while also delivering useful information for conservation of these ancient and endemic frogs, the researchers maintained.