Maxima clam retracted mantle

[wii64brawl]

I've had this guy for about four months now. He has been doing great and has shell growth. I noticed this morning though that part of his mantle is retracted. The rest of him looks good: quick reactions, good extension otherwise, tight byssal grip, no gaping. I thought it could be pinched mantle, but the rest of his mantle looks fine and shows no signs. I'm thinking he could have been irritated by something in the tank last night, especially since I did some maintenance. Though I'm not too sure. Does it look like PM to anyone?

 

[wii64brawl]

Anyone?

 

[jda]

PM is usually on one side or another, and it looks more pinched than retracted. This looks more like to me the first day of the end, but that seems weird if you have new growth since that is the only positive-positive with clams. I dunno what to think.