Center for Biological Diversity

For Immediate Release, June 22, 2023


Tierra Curry, (928) 522-3681,

Lawsuit Seeks Final Endangered Species Act Protection for Pyramid Pigtoe Mussels

Imperiled Freshwater Mussels Found Across Nine Southern, Midwestern States

NASHVILLE, Tenn.— The Center for Biological Diversity sued the U.S. Fish and Wildlife Service today for failing to finalize Endangered Species Act protections for a freshwater mussel called the pyramid pigtoe which has disappeared from nearly 80% of its range.

The Center and allies petitioned for protection of the mussel in 2010. It was finally proposed for protection in September 2021 but is still languishing in bureaucratic limbo.

“Freshwater mussels are at the forefront of the extinction crisis in the United States as we’ve already allowed 36 species to be lost,” said Tierra Curry, a senior scientist at the Center. “We need to take urgent action to protect the pyramid pigtoe while we still have time to save them. The Endangered Species Act is a powerful tool that can stop extinctions, but it only works when we safeguard the places wildlife need to survive.”

Currently found in Alabama, Arkansas, Kentucky, Louisiana, Mississippi, Ohio, Oklahoma, Tennessee and Virginia, the freshwater mussel was once found in 151 populations but now survives at only 35 sites.

The pyramid pigtoe, also known as the pink pigtoe, is reddish to chestnut brown with a smooth thick triangular shell that can grow to almost 4 inches. It declined because of historical collection of shells to make buttons on an industrial scale followed by widespread damming of rivers and the spread of invasive species like zebra mussels. Pollution from suburban development, agriculture, mining and dredging have all degraded water quality and harmed freshwater communities. Pollution also makes mussels more vulnerable to diseases including a novel virus that is causing them to die off.

The pyramid pigtoe has already disappeared from Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Pennsylvania, West Virginia and Wisconsin. It is found in medium to large rivers and is still occurring in the Arkansas-White-Red, Lower Mississippi, Tennessee and Ohio river basins. Pyramid pigtoe individuals may live up to 45 years in good habitat.

Freshwater mussels improve water quality for people by filtering algae, bacteria and pollutants out of rivers. Their shells stabilize river bottoms and provide housing for other animals. The pyramid pigtoe reproduces by releasing packets of fertilized eggs into the water where minnows try to eat them. The packets burst and the larvae attach to the fish’s gills to grow. Once the mussels develop tiny shells, they drop off onto the river bottom to begin life on their own.

In addition to the pyramid pigtoe, today’s lawsuit includes 12 other species from around the country unduly waiting for protection: the cactus ferruginous pygmy owl, tall western penstemon, Mt. Rainier white-tailed ptarmigan, Peñasco least chipmunk, the Humboldt marten, six Texas mussels (Texas fatmucket, Guadalupe fatmucket, Texas fawnsfoot, Texas pimpleback, Guadalupe orb and false spike), and four distinct populations of the foothill yellow-legged frog.

Pyramid pigtoe mussel. Photo by Matthew Patterson, U.S. Fish and Wildlife Service. Image is available for media use.

The Center for Biological Diversity is a national, nonprofit conservation organization with more than 1.7 million members and online activists dedicated to the protection of endangered species and wild places.

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