Mussels are sea or river mollusks. Due to the great popularity around the world, in some countries they have created whole farms in which mussels are grown. There are several options for selling mussels, the farther the farm, the deeper the freezing. Sometimes mussels are sold peeled and frozen, they are already processed. If you are going to add mussels when cooking this or that dish or just pickle the clams, peeled mussels will do just as well and will be just as tasty.