Researchers have found a new family of eel-like fish, named dragon snakeheads, which live in underground waters in southern India. These primitive fish are a type of “living fossil” and may have diverged from their nearest relatives more than a hundred million years ago.

Discovering a new family of fish—the taxonomic category above genus and species—is very uncommon, says study leader Ralf Britz, an ichthyologist at Senckenberg Natural History Collections, part of the Museum of Zoology in Dresden, Germany. Taxonomic families are often large and diverse; For example, the human family, Hominidae, includes chimpanzees, orangutans, and gorillas.

This family includes only two species, one of which is named the Gollum snakehead, after the subterranean Lord of the Rings character.

“We think this is the most exciting discovery in the fish world of the last decade,” says Britz, lead author of a study published recently in Scientific Reports.

These strange, long-bodied fish, which dwell in aquifers of porous rock, are rarely seen, only coming to the surface after flooding from heavy rains. Britz says the family’s common name is fitting because “everyone who sees a photo of the fish is somehow reminded of a dragon.”

The area where the fish live, the Western Ghats of southern India, is a biodiversity hot spot. In all, scientists have discovered 10 species of subterranean fish in the aquifers there that provide water for millions of people.

An estimated six million wells draw from this underground reserve, Britz says. This has lowered the water table and could imperil some of the newfound obscure species that live there.

Enigmatic species

The saga began in early 2018, when researcher Rajeev Raghavan, a study co-author and fish researcher at Kerala University of Fisheries and Ocean Studies, spotted a post on Indian social media from a person who found and photographed an odd fish retrieved from their backyard well.

Raghavan sent the photo to Britz, who had “no idea what it was,” Britz says—not the species, genus, or family. Britz travelled to India after Raghavan and other colleagues had collected more specimens, to scientifically describe the fish.

An initial study, published in Zootaxa in May 2019, identified the fish as a new species and genus, named Aenigmachanna gollum—the Gollum snakehead. Shortly thereafter, another researcher found a second species in that genus as well, based on a single specimen—the Mahabali snakehead.

Another breakthrough came when Britz and others visited a farmer’s field north of Kochi, a town in Kerala. There, late at night, they found Gollum snakeheads surfacing into a flooded rice paddy.

But when Britz and his colleagues performed further research on the anatomy and genetics of these fishes, he found they belong in a new family entirely. His genetic analysis shows they may have diverged from their nearest relatives, snakeheads in the family Channidae before Africa and India separated and spread apart 120 million years ago, Britz says.

There are more than 50 species of Channidae snakeheads, which live in streams and lakes throughout Asia and Africa.

Strange fish

The dragon snakeheads have “a whole series of primitive characteristics,” and are rightly called “living fossils,” says David Johnson, an ichthyologist at Smithsonian’s National Museum of Natural History in Washington, D.C., who wasn’t involved in the paper.

These unique traits include a shortened swim bladder and fewer vertebrae with ribs, features that show the dragon snakeheads are less specialized than regular snakeheads.

The family also lacks a structure called a suprabranchial organ, which allows Channidae snakeheads to breathe air. This air-breathing trick has enabled one species, the northern snakehead, to spread far and become an invasive nuisance in North America and elsewhere.

Dragon snakeheads also have eyes and a reddish-brown pigmentation—traits uncommon in subterranean fish, many of which are white and eyeless.

Britz says it’s unclear why the species have these traits but suggests it may be because they are not exclusively subterranean.

These fish have a unique way of moving in the water, undulating their fins as eels do to move backwards and forward. This probably helps them get around in small underground chambers. Watching them can be mesmerizing, Britz says—they move “like a veil in the wind.”

Johnson likens the dragon snakeheads to a primitive eel-like fish named Protoanguilla palau, discovered in an undersea cave in Palau, which he helped describe in a 2012 paper. Like the dragon snakeheads, this previously unknown family of eels has ancient traits that have been lost in its relatives, and it has changed relatively little over time.

Why such living fossils survive without diversifying much remains a mystery. “I can’t begin to understand why,” Johnson says.