EL PASO, Texas— The Center for Biological Diversity sued the U.S. Fish and Wildlife Service today for failing to designate critical habitat for the endangered Texas hornshell, a freshwater mussel once common across the Rio Grande watershed in Texas and New Mexico. Today the species occupies just 15% of its historic range.

“Without protection for the places they live, the Texas hornshell could soon vanish forever,” said Graham Rex, an attorney at the Center for Biological Diversity. “These mussels are living water filters that help keep the rivers of the Southwest clean, clear and healthy. If we lose the hornshell, we lose a vital guardian of the Rio Grande River system.”

After a 2004 petition from the Center and a coalition of scientists and authors, the Fish and Wildlife Service protected the hornshell under the Endangered Species Act in 2018. Federal law required the agency to designate critical habitat for the species within one year. Although the Service proposed critical habitat in 2021, that designation has not been finalized.

Texas hornshells typically live in narrow areas of rivers and streams with sand, clay or gravel bottoms. They anchor themselves in undercut crevices, boulders and riverbanks where currents slow, providing a safe foothold during high flows.

The greatest threat to the species is habitat degradation and loss. Groundwater pumping, drought and chemical contamination have caused the hornshell to disappear from much of its historic range. Climate change is also expected to intensify those pressures by worsening drought and reducing river flows throughout the Southwest.

Freshwater mussels are the most imperiled group of animals in the U.S. More than 70% of North America’s nearly 300 mussel species are listed as imperiled, with at least 35 already presumed extinct.