Critter ID(No Pic)

[Midus]

I've only noticed around 3 of these things. They're all white and look something like cotton balls attached to my Live Rock. The largest one is about a half an inch wide. I've noticed a small hole on top of them. They don't move at all.

[bertoni]

That sounds like a sponge, possibly a Scypha. Might be a tunicate, if there's one other small opening.