Margaritifera margaritifera, commonly known as the freshwater pearl mussel, is a bivalve mollusk found in clean, cold rivers and streams across Europe and North America. This species is notable for its ability to produce pearls, which form around irritants inside its shell. The mussel has a long lifespan, often living over 100 years, and plays a crucial role in freshwater ecosystems by filtering water and providing habitat for other species. The life cycle of Margaritifera margaritifera involves a unique relationship with salmon and trout as hosts for its larvae, known as glochidia. These larvae attach to the gills of fish, where they develop before eventually dropping off to settle on the riverbed. Unfortunately, this species is threatened by habitat loss, pollution, and overfishing, leading to significant declines in its populations.