I recently (5 weeks ago) purchased a 4" crocea that i found out later was a wild caught Vietnamese clam. Anyhow, I hadn't looked too closely at the mantle upon purchase, but realised when I got it home that I could make out 6 tiny white pin-point spots on the mantle. I grew extremely concerned and wound up emailing Daniel Knop wondering what it was and if perhaps it could be the dreaded white spot clam disease. He thought not as the white pin point spots were not raised. Well, I put the clam in a Q tank for 3 weeks for observation and I noticed the spots slowly changing> They went from a distinct pin-point white spot to a blurred blotch maybe 3* the original size, and appeared more of a faded grey. Was it some sort of mild bleaching due to stress? I don't know....but, those faded spots gradually disappeared as well and now the mantle is completely free of any irregularities. I also saw another larger area of bleaching beginning on the outer edge of the mantle in one spot, this has completely disappeared as well. The clam seemed to improve once I moved it out of the Q tank (96 watt PC's only) and just left it alone in my main tank (400w MH) which is a pretty stable environment. I don't know what caused this, but I would guess stress from shipping (at least in my case).
Have you noticed any changes in the spots with respect to size or number?