what is this on my Live rock?

[fredflinstone]

Hi. I saw one of this growing on one of my live rock. Later this started growing in other rocks as well. Can someone tell me what exactly is this?

I have the picture in "my galary"

 

[yibs]

http://www.reefcentral.com/forums/showthread.php?s=&threadid=514384

 

[stars&stripes]

Will puffers eat aptasia in a fowlr?

 

[fredflinstone]

Hey yibs. Thanks for the tip man. I have uploaded a second pic. This is whitish looks like a small mushroom.
CAn you please let me know what this is?
And also in one of the live rocks, I see sometihng whitish that comes out and after a while goes back in. Like a stinger or something. It comes out and stays for a while. Ina jiffy vanishes or rather retracts back in.

Please let me know what this could be.
Thanks in advance.