Mussels are relatively cheap at the seafood counter and they taste delicious. When you steam their shells open, the liquid is so delicious. To me, it tastes almost more like the ocean than cooked clams. These are served chilled although they can also be room temperature. Make the salsa in advance and cook the mussels when you are ready. I love the peppery arugula combined with the basil in the salsa; these flavors bring out the natural sweetness of the mussels!