help id. what is this?

[big deddy]

Just noticed this on 2 of my rocks. Any ideas on what it is? Harmful? Could it be a sponge? How can I get rid of it?

 

[saltyphish]

Looks like a sponge to me. I would not worry about it. Sponges usually go away on their own. Though I did have a outbreak of pineapple sponges in my tank and they would grown in my zoas. At first I tried to remove them but eventually stopped since they did not seem to harm them.

 

[big deddy]

I have a couple sponges on another rock. I dint know how the reproduce so I was a little concerned. Thanks for your reply