Here's the step by step information when a mussel is disected.
http://www.uwlax.edu/biology/Zoo-Lab/Lab-06/Mussel-Shell-1.htm
Here's a video of a mussel disection.
http://www.lookfordiagnosis.com/videos.php?title=Clam+(Mollusca)+Dissection&content=Mt.+SAC+Bio+2+dissection+of+a+Clam&lang=1