They are small enough that the camera wont focus on them so all the pictures are blurry. They are about the size of a pinky finger nail and a white color. The person I got the rock from has alot of them and I think they eat algea but not sure.
either asterina stars, if you're lucky it's a load of brittles.
if it's the former, you might find they can reproduce to plague proportions.
i had my tank taken over once
perfect excuse to set up a nano for harlequin shrimp, heh heh.