Unidentified spaceball in my tank

[colcoral]

Check this out. It is growning under some of my rock. It is about the size of a quarter and kind of resembles a wasp nest. I am thinking some kind of eggs are in there. I hope they aren't galls, but whatever this isn't it build the bubble, it's not growing in another coral. It looks like a little critter is crawling out of the very top right hole. Any ideas??

 

[fisherson]

looks like a sponge to me. It's harmless

 

[colcoral]

I do have a lot of volunteer sponges in my tank, but this guy looks like he is full of critters. I wish I could get a better pic, but it is under a ledge. Thanks for the input.