Muscles move the gastric mill. The gastric mill is a gizzard that is found in the majority of decapod crustaceans.

In crustaceans, specifically decapods such as the crayfish, the stomach is divided into two parts: the first, or anterior part is called the "gastric mill". The gastric mill is lined with chitinous teeth which grind up coarse food particles. The posterior part of the stomach acts as a filter to keep coarse particles from entering the digestive glands, where absorption takes place.

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No, crabs do not have teeth in the sense that most people think. They have tooth-like structures in their stomachs in a chamber called the gastric mill which performs food processing, just like the teeth in your mouth. Unlike your teeth, the teeth in a crab's gastric mill are not made of bone, but of a material called chitin, which is the same material that makes up most of a crab's shell.

The gastric mucosa is located in the stomach. In humans the gastric mucosa is approximately 1 mm thick with a smooth and soft surface.