If it is moderate amount of light, and the water is good, it may disappear after a few days. Check for parasite (rice snails). Does it show good growth in past few months?
Gasping should be watched, but sometimes, it is temporary. Good luck.
I think my angel may have took a small taste. I hope not, I have seen it pick the polyps from my pollicipora but thought that was the extent of it. I have had this clam for asome time and will yank that angel in a heart beat if I have to. It is a rusty angel. I will have to keep an eye on it.
Supposedly, it's common in Crocea, but it's still a good indicator that something could be wrong. The best indicator is when they don't react quickly to movement.
You would think that a completely healthy clam would have so much tissue mass, that it would be difficult to gape at all.