clam health

Is this maxima dying…? It is not fully extending since bought on 4/15, and today it suddenly show very gaped mouth (you can see white flesh inside), the mantle is very retracted, and barely react to light shade… anything I can do to save it?

Hello! I'm a new clam dad and I recently picked up this Derasa clam about 3 days ago. I love this thing to pieces but I noticed its Incurrent Siphon has been gaping the past two days... I've been watching it like a hawk to make sure it didn't show any other signs of unhappiness but I can't...