Ganoid refers to a type of fish scale that is hard and shiny, often found in certain ancient fish species. These scales are made of a bony layer covered by a layer of enamel-like substance called ganoin, which gives them their distinctive appearance. Ganoid scales are typically found in fish like sturgeons and gars. Unlike the more common cycloid and ctenoid scales, ganoid scales are thicker and provide better protection. They are often diamond-shaped and overlap like armor plates, helping these fish survive in their aquatic environments. Ganoid scales are a key feature in the classification of certain fish groups.