When the crayfish is not walking how does water move over gills?

When a crayfish is not walking, it uses a different mechanism to move water over its gills. Instead of relying on the movement of its walking legs, it uses a specialized structure called the scaphognathite. The scaphognathite is a flap-like appendage located at the base of each maxilla (mouthpart). When the crayfish opens its mouth, the scaphognathite moves outward, drawing water into the branchial chamber. When the crayfish closes its mouth, the scaphognathite moves inward, forcing water out of the branchial chamber and over the gills. This process creates a constant flow of water over the gills, which allows the crayfish to extract oxygen from the water.