They look like tiny white polyps, at the very top of the picture. They close up when the lights go out, and are open during lighting hours. There seems to be 6-8 all in the area the size of a quarter.
They came with the live rocki purchased. They were tiny but noticeable in the beginning. They have become larger, but not large enough to identify yet. Time will tell.
I do not believe they are snail eggs. they were definitely hitch hikers, , and the rock has been in the tank 6+ weeks.
I would guess sponges, but hoping for fan worms. Time will tell though.