What snails are these?
 

So my orange plate been losing some flesh for about a month now so I moved it to my sump(frag tank) to let it heal without my shrimps picking at it to make things worse. Today while doing a water change I notice a bunch of these snails I never seen before or mybe just never looked close enough to find out. They are only on the areas of dead tissue. I took a macro shot of it via iPhone. Please identify if they are bad or not n if they r eating my plate or cleaning the dead tissues

http://i1292.photobucket.com/albums/...psjlvjgkhy.jpg

Any1 know if these snails r good or bad?

I have no idea what they are, but I'll hazard a guess that they are eating the algae from the dead parts