What is this!?


Reefing newb
I got my tank a while back....it has been doing great and it is fun to watch my live rock grow...we only have now three hermit crabs, several feather dusters, a top snail and of course my bristle worms( never had fish since I rescued it)....How ever...

A few weeks ago I noticed a round furry whiteish pale green ball on my live rock...about the size of a dried out pea. From then till now it has slowly moved at least 4 inches to the top of my live rock....Now today I see there is another one on the back side of my live rock and it is bigger then a kernle of corn. But it is still the pale green white color and furry looking almost like a ball of mold. What in the heck is it and what do they do? It obviously is alive if they can move up the rock.:question: I did a search on here and can't find anyone with one....Shaz
Digging through lots of photo's I finally found something that closely resembles what I have in my tank. They are sponges..of some sort. Here are pictures of my furballs...Shaz