Foraminiferans is another possibilty. These usually protrude from the rocks a little, but they don't start off like that.
Btw you might want to add another one of those pumps to the tank. I'm not sure what the GPH of that thing is, but for some reason I don't think it's enough. You definitely want tings to be on the turbulent side when it comes down to flow in a reef tank.