굴, or oysters, are marine mollusks found in both saltwater and freshwater environments. They have a hard, irregular shell that protects their soft body inside. Oysters are known for their ability to filter water, which helps maintain healthy aquatic ecosystems. They are also a popular seafood delicacy enjoyed in various cuisines around the world. In addition to being a food source, 굴 play a significant role in the environment. They form reefs that provide habitat for other marine life, such as fish and crabs. Oysters are also harvested for their pearls, which are formed when an irritant enters their shell, leading to the secretion of layers of nacre.