well, i hope I don't get the answer I think I am going to get... I picked up the clam when I got home from work to inspect it, and it opened up shortly after lights on (I'm on reverse photoperiod at the moment). The color still looked good, but mantle still in the shell. I turned it over to see if anything was possibly irritating the foot (it's been in the sandbed), and the foot looked horrible!!
instead of looking smooth and kind of like a scallop type texture, it looks almost cottony. Hopefully this pic will help. The little white dots are pieces of sand.
I put him on a rock on the sandbed with the little plastic thingy over him. Is he too far gone? He's still opening & closing & not brown. Is there ANYTHING I can do to save him?