Cotton balls?

[tah532]

For over six months now i have these dime size, cotton ball looking, white puffy things on the underside of my liverock. Sorry for not having a pic of them. Does anyone know what they might be?

 

[Anonymous]

Species of Porifera (sponge).
Harmless filter feeders.

mario

 

[tah532]

Ok, sounds good thanks!