Cocoon on live rock

[luvmytankmoretu]

I have a cocoon like growth on my live rock, originally thought to be a sponge; today there is a hole burrowed in it. Can anyone tell me what it is? The attached photo is blurry, but you get the idea.
s?

 

[btldreef]

Still think that it's probably just sponge, it might just be starting to break apart.

 

[luvmyreef]

Yep. Agree. Sponge.

 

[luvmytankmoretu]

Thanks, that makes me feel better!