A mussel is a type of shellfish that lives in water, with a dark, oval shell made of two hinged pieces. Mussels attach themselves to rocks, docks, or other surfaces using strong, thread-like fibers called byssal threads, which work like natural superglue to keep them from washing away in currents and waves.

Freshwater mussels live in rivers and lakes, while saltwater mussels live in oceans. They're filter feeders, meaning they pump water through their bodies and strain out tiny particles of food. A single mussel can filter several gallons of water per day, which helps keep waterways clean.

People have eaten mussels for thousands of years. They're often steamed and served in restaurants, sometimes in a broth with garlic and herbs. The word can also describe the meat inside the shell.

Scientists pay close attention to mussel populations because these creatures are sensitive to pollution. When mussels thrive in a river or lake, it's a sign of healthy water. When they disappear, it can signal environmental problems. Some freshwater mussel species can live for over a century, quietly filtering water and supporting the ecosystem around them.