It does look like separate parts of the mantle are retracting which is what happens in pinched mantle, but it's so closed that it's hard to tell. Was it always that way, or did it gradually kind of shrivel up? Mine gradually shriveled, but it never retracted that far.

When I've done my FW dips, I adjust the temp by floating a bag in aquarium water for a half hour or so and then adjusting the pH to the same as the tank. I then dip the clam for about 10-15 minutes, although I have heard of some people doing it for over an hour. The clam closes up and is ticked off during the treatment, but the next day it's always looked much better. I've now done 3 FW dips for both my maxima and crocea clams.

It's a protozoan that causes pinched mantle, and the only way to cure the infection is to set up a hospital tank and treat with metronidazole. The FW dips just kill off some of the bugs, but don't get rid of the infection. Anyway, I'm about to set up my hospital tank very soon. Just need to get rid of some live rock so I can fit some stuff in there!

Good luck with your clam, hopefully you can figure out what makes it happy.

Matt