Strange growth on rocks

[Mugatu]

A week or so ago I noticed something growing in a low light high flow area of my tank that I couldn't find any pictures of online to match it for an ID. The majority is under the rock and has some stringy things extending up. In the case the pics arent very ckear it is white and soft. I think it might be a kind of sponge but am not sure. Have only been reading for about 9 months do a lot is very new to me.

It started on dry rock that i added to the tank a couple months ago. Has been growing steadily since I noticed it and I want to know if I need to start working on getting it cleaned off or if it is ok to leave.

 

[manfrog]

Spaghetti worm?
Harmless (in my experience) but I understand it is possible for them to irritate corals. I have never tried to remove them but google 'spaghetti worm' and see what you think.

 

[AlSimmons]

If these "strings" aren't moving around independently looking for food then what your seeing are probably just harmless sponges.