A team of scientists has come across a tadpole burrowing through sand in India's Western Ghats.

The team of Gayani Senevirathne from the University of Peradeniya and his colleagues deemed the discovery a fascinating one, as tadpoles would not usually burrow through sand or swallow that material.

The remarkable tadpoles - found deep in streambeds where they exist in complete darkness until fully developing into froglets — belong to the Micrixalidae or Indian Dancing frog family. The researchers genetically confirmed their identity as Micrixalus herrei.

Study author and professor SD Biju of University of Delhi said that this is the first documentation of tadpoles in this frog family, as only adult dancing frogs had been seen over the last century.

"These tadpoles probably remained unnoticed all these years because of their fossorial nature, which in itself is a rare occurrence in the amphibian world," he reveals.

Indian dancing frogs are known to sit on boulders in streams while they wave their legs as a means of sexual and territorial display. The tadpoles of this family, however, had remained mysterious to scientists - in fact the only one among frogs and toads that maintained such mystery.

But the biologists ventured to know these tiny creatures better. The tadpoles are characterized by skin-covered eyes for protection from abrasion while they burrow through gravel beds, as well as muscular eel-like bodies.

Although they lack teeth, they retain well-serrated jaw sheaths, which help block large grains of sand from entering their mouths during feeding and movement.

Their gut, too, contains small grains of sand and decaying organic stuff acting as nutrient sources.

A double staining procedure that scrutinized the tadpoles' bones also showed they have ribs that provide increased muscle attachment to help them navigate through sand. "Lime sacs" or white globular sacs containing calcium carbonate are another feature of these tadpoles that are barely seen in other frogs.

There had been very little known about the habitat requirements of the tadpoles. Current observations, though, revealed that they live in sandy banks under canopy-shielded streams.

These findings confirm the unique amphibian showcase of the Western Ghats, which is considered a biodiversity hotspot and a good source of information for frog conservation.

The findings were published March 30 in the journal PLOS ONE.