Gills are specialized organs found in aquatic animals, such as fish and amphibians, that allow them to extract oxygen from water. They are typically located on the sides of the head and consist of thin filaments that increase the surface area for gas exchange. Water flows over the gills, and oxygen diffuses into the bloodstream while carbon dioxide is expelled. In addition to fish, some invertebrates like crustaceans and mollusks also possess gills. These organs are essential for survival in aquatic environments, enabling these animals to breathe underwater. Gills play a crucial role in maintaining the balance of oxygen in aquatic ecosystems.