1. Peel and devein shrimp (see Shrimp Basics). Cut the shrimp crosswise into 2 or 3 pieces.
2. Pull the wiry beard, if any, from the flat side of the mussels. Rinse the mussels well under cold water and drain. Combine the mussels and ½ cup cold water in a 2-quart saucepan. Set over high heat and cover the saucepan. Steam (