What snails are these?

[jason604]

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