What are these white tenticles

Anyone know what these white tenticles are? I would say they have been growing even though they are on the bottom side of this rock.

 

Looks like some kind of sponge IMO.

 

I wouldnt worry to much about that...i would just watch it, but like if it stays small and doesent grow to be amazingly huge very fast! i wouldnt worry

 

+1 on the sponge. Saw a ton of it at an LFS & specifically asked what it was just for this thread LOL. And when I say a ton, I mean a ton. A couple of tanks it was all over the place. And they were VERY healthy tanks.

 

Thanks for remembering, it is starting to spread but since I don't have many corals I don't mind. It is also starting to look a little pink.

 

The stuff in the display tanks at that store was all over the place. It looked like a plant or a colorless coral out of control LOL. They just leave it alone, and I didn't think to ask if it could be removed. I mean, their tanks were 250 gallons, 300 gallons, and a huge, shallow frag tank, so I don't think they were as concerned as someone with, say, a 55 gallon tank might be.

 

if it turns red i would say macro algae, but thet reachers at the end of it almost looks like a coral, xenia.