What the heck is this????? (live rock)

[stantheman]

Noticed my population of bristle worms exploding thinking that is what this little sac looking thing is but how about this weird white hairy stiff growing everywhere on my rock? Let me add it's only on one rock!:headwalls:

[Betta132]

Both look like some sort of sponge. If so, they're both harmless.

[stantheman]

Thanks I hate not knowing ha

[Tangnerd]

I used to have that stuff growing all over my rock too. Eventually it just naturally went away.

[faithenfire]

the first one is a sponge. the second one may be as well but not sure. the first one is harmless at least has been in my tank