What is growing in my tank?

[Aliu]

Hi guys. I came back a bit late tonight from work and was looking into my tank when I saw something very weird.

Please see attached for pictures. I have no idea what this thing is. It is white/fuzzy looking but also somewhat transparent. It is growing between 2 of my live rocks.

I did not notice this yesterday. Any suggestions on what it is and if it should be removed or safe to leave in the tank?

 

[cperry7467]

Looks like a pineapple sponge

 

[JMLewis]

Looks like a sponge to me, harmless.