White stuff on my live rock

I have a 15 gal tank, water capacity 18 gallons. Two false perculas, 17lbs of live rock, 20lbs of live sand. Its been up and running for about 3 months. This white blob showed up about a week ago and has been slowly growing. I think its a sponge but im new to the sw world. Any ideas?

 

Looks like a sponge to me.

 

could also be feather duster worms spreadin their tubes

 

feather duster tubes. look for ends of the tubes and there should be holes.

 

Are you talking about the white lines or the white blobs?

The lines are from tube worms, and the blobs are sponges.

 

ohh the blobs... yea sponges like stepho and jkuja said

 

Thanks for the confirmation. I'm talking about the large whitish blob not the white tubes. Those seem to be all dead.