I dont think it looks like it is gaping too terribly. The crocea's at my store, when they have gaped, you will definatly know it. I also think the quality of the pic does not give the clam justice.
I would really refrain from feeding Marine Snow that often. The stuff has given myself and my clients more problems than not. If you want to feed your tank anything try Dt's and do it every few days. That constant buildup of additional organic compounds in your tank cannot be good for the...