Weird growth on rocks

[sezaro21]

Hello everyone. I have a weird growth that I noticed on one of my rocks. Can't tell what it is. Is anyone able to tell me what these are and if they are bad for my tank? It's only on this one rock and no where else in the tank.

 

[Reefkeepers Archive]

Sponge, harmless filter-feeder

 

[Waters]

Looks like a sponge....harmless filter feeder. I have them in my tank as well....they normally grow in dark, shaded areas.

 

[vlangel]

I also have similar white-ish sponges in my tank, especially in the shadowed areas.