Clams don't do a lot. They sit at the bottom of a lake and move very slowly across the sandy floor. They have an appendage called a foot they use to slowly move and they have have another appendage...
Shells and all? Sure, you could but, most people are put off by crunchy chowder. If you mean that you plan to substitute fresh clams into a recipe that calls for canned clams, of course you can.