Is this a sponge?

[NavyNano212]

It's been growing slowly over the past two years, nestled inside the live rock that my green polyps having been growing on for almost 8 years...
You can't see it, but the other end has a hole in it...
I think there is a mussels growing in the back as well...

Thanks

 

[rookie07]

Sponge or tunicate, hard to tell.