Crayfish and their relatives, lobsters, crabs and shrimp, have similar digestive systems that feature two-part stomachs. Called malacostracans, these animals consume food with their mouths and pass the food through their stomachs and intestines before finally expelling it through the anus, according to the University of Michigan's Animal Diversity Web.
Inside the stomach, crayfish have a structure called a gastric mill. The gastric mill helps to grind food items into small pieces. Crayfish consume a wide variety of foods, including vegetative debris, fish and aquatic invertebrates. Crayfish capture food with their large claws before lowering it to their mouths, where they consume it.