Orange-Footed Pearly Mussel
(Plethobasus cooperianus)

Habitat: This mussel prefers clean, fast-flowing water in silt-free rubble, gravel or sand of medium to large rivers. It buries itself in sand or gravel in water as deep as 29 feet. Only the edge of its shell and its feeding siphons are exposed.

Behavior: Reproduction requires a stable, undisturbed habitat and a sufficient population of fish hosts to complete the mussel's larval development. When the male discharges sperm into the current, females downstream siphon in the sperm in order to fertilize their eggs, which they store in their gill pouches until the larvae hatch. The females then expel the larvae. Those larvae which manage to attach themselves to the gills of a host fish, grow into juveniles with shells of their own. At that point they detach from the host fish and settle into the streambed, ready for a long (possibly up to 50 years) life as an adult mussel.

Why It's Endangered: Dams and reservoirs have flooded most of this mussel's habitat, reducing its gravel and sand habitat and probably affecting the distribution of its fish hosts. Reservoirs are fatal to most riverine mussels; one researcher counted 45 mussel species in a river before the construction of a dam. Four months after the dam was completed, he could find none. Dams and reservoirs are barriers that isolate upstream populations from downstream ones.

Other threats include pollution from agricultural and industrial runoff, and siltation following deforestation. These chemicals and toxic metals become concentrated in the body tissues of such filter-feeding mussels as the orange-footed pearly mussel, eventually poisoning it to death.

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