Lurking in waterways with its long, slimy body and beady eyes, the hellbender is Tennessee's largest salamander, not to mention a survivor of ancient times.
For at least the last two decades, though, as water quality in many parts of the country has declined, the hellbender's population has dwindled, threatening its very existence, wildlife advocates say.
Recently, the Tucson, Ariz.-based Center for Biological Diversity filed a lawsuit in federal court in Washingtonagainst the U.S. Fish and Wildlife Service for failing to protect hellbenders under the Endangered Species Act.
Once abundant in East Tennessee, the threatened hellbender has been listed by Tennessee wildlife officials as being "in need of management." The lawsuit seeks to force the federal government to move more aggressively to protect the animal from harm.
The suit does not explicitly seek to place hellbenders on the endangered species list, since there are several hoops to jump through before a species is listed. Instead, the suit asks federal officials to set a deadline for a final study on hellbenders and eight other species regarding their endangered status.
In 2011, the Center for Biological Diversity reached a settlement with the Fish and Wildlife Service under which the agency must make a decision on some 800 imperiled plants and animals by 2018.
The lawsuit, which was filed in late June, is the latest legal maneuver emanating from the settlement.
Stacy Shelton, spokeswoman for the Fish and Wildlife Service, said hundreds of species are farther along in the process than the hellbender. She said a final determination on the hellbender will not be made any time soon.
"Our capacity is being tapped out by the multidistrict litigation," Shelton said of the 2011 settlement.
The Service, Shelton said, has an emergency measure to speed up the process if a species is on the brink of extinction. She said the situation facing hellbenders is not that dire.
The settlement's impact has been huge. If many of the more than 800 species listed gain federal protection, the endangered species list could grow by more than 50 percent, activists say, triggering new battles in court.
The U.S. Fish and Wildlife Service's initial study shows that there may be cause of concern. After the center submitted a petition to them about the hellbender, wildlife officials concluded that installing protections for the hellbender "may be warranted" - essentially advancing the hellbender to the next stage.
Congress passed the Endangered Species Act four decades ago to protect animals, insects and plants threatened with extinction. It has led to exhaustive legal battles between wildlife advocates and business groups over various species, with both sides registering wins.
While the suit also seeks reviews on Sierra Nevada foxes, Panama City crayfish and others, protecting hellbenders is an especially popular cause, according to Tierra Curry, a conservation biologist with the group that is suing the Fish and Wildlife Service.
"We chose to prioritize the hellbender because it's so sensitive to water pollution that it's an umbrella species for protecting entire watersheds," Curry said. "If we protect streams and rivers for the hellbender, we will also protect the other species that share its home, as well as high water quality for people."
Gaining endangered species status starts with a petition that summarizes all the research and scientific studies around the population of a species. Federal officials can either grant or deny the petition. If granted, there is a second review stage before three species specialists issue opinions. Barring any serious resistance from the panel, the species is added.
Hellbenders, and more than 500 other species, are waiting to advance beyond the second review stage. They moved beyond the initial review phase nearly three years ago.
The Fish and Wildlife Service in 2011 listed the Ozark hellbender, found mostly in Missouri and Arkansas, as endangered.
The Nashville Zoo has for several years been breeding Eastern hellbenders using artificial fertilization. Researchers found that nearly all the hellbenders they were finding in Tennessee streams were old males, which is a less than ideal mating state. To address the problem, the Tennessee Wildlife Resources Agency gave the zoo a $32,000 grant to breed hellbenders.
Dale McGinnity, curator of cold-blooded animals at the zoo, has said that the hellbender fossil record goes back to the age of dinosaurs.
Breeding them, though, is difficult due to how long they take to mate - males can wait until they're 10 years old before they reproduce.
In nature, hellbenders are creatures of night, when they hunt for small fish and crawfish. By contrast, fish, turtles and snakes prey on hellbenders. Occasionally they are caught inadvertently by anglers.
"They're such a charismatic species," Curry said. "Many have an emotional response to them. We're really hoping to get some protections in place before it's too late."