Also note that often times a shrimp can "smell" trouble in the tank and are the first ones to the "Scene". It's possible something is wrong with the clam but also possible you have a bully shrimp. I used to notice that my peppermint shrimp would pick at my new Sea Hare. I let it go and it finally "expired". At first it was thought that maybe the picking LEAD to it's demise but more rational thinking leads me to think the shrimp was just there a tad bit early because it could "smell/sense" what was happening.
Good luck and Happy Reefing
