Osteichthyes, commonly known as bony fish, are a diverse group of fish characterized by a skeleton primarily made of bone rather than cartilage. This class includes two major groups: Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish). They possess a swim bladder for buoyancy and gills covered by an operculum, which aids in respiration. Osteichthyes are the most numerous and varied group of vertebrates, found in a wide range of aquatic environments.