Are they hard and immobile? My guess is mini feather dusters. If thats the case they are harmless and cool to watch. If thye move around they might be a bad thing ...
If they do move, they may be baby snails, pods, some other normal little critters, or could even be flatworms.
If they don't move, then featherdusters are likely. Feather dusters will look like a little coiled shell, and if you look closely a little fan like thing will come out but retract quickly if distrubed. Could also just be coralline algae starting.
Try to really look at them and describe in the most detail you can.
No they do not move around. hmm... i'm a little concerned now, hope fully it's not parasite or anything harmful to both me and fishes.
I see my clown fish eat them all the time. Also this thing happen at the same time as brown and green algea appear. This is brand new tank that recently established.
The white oval has lighter color surroding its brownish inner circle. I really can not tell if they are seeds or eggs.
Oops, no one mentioned that feather dusters are cool
Could also be vermitid snails, which also look like a kind of calcerous coil, but insted of a "fan" they send out a "mucus net" that traps food/detritis. Vermitids are sometimes a little unsightly and can be a slight nusiance, but nothing to worry about really.