Scallops are touchy anyway as filter feeders and I think most woud say they don't have a good long term track record. They are filter feeders and seem to need a constant source of food along with good water quality. These two things are to provide simultaneouly. My guess is they died and the hermits, urchin, and shrimp did what they do.
I've had Baggais and PJ cardinals with a deresa clam as well as with several corals. The only thing I've seen them go after was pods
. I imagine they might see smaller shrimp as items ont he menu.