The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (dinosaurs, birds, pterosaurs, crocodiles and alligators), earthworms, some gastropods, some fish and some crustaceans. This specialized stomach constructed of thick, muscular walls is used for grinding up food, often aided by particles of stone or grit. In certain insects and mollusks, the gizzard features chitinous plates or teeth.