Is this a type of sponge?

[FunWithFishes]

After a year away on work field assignment and have my tank set back up! As I come to the end of my cycle, I noticed what I thought to be sponges.

However, they have a large hole in them that makes them different then the sponges I have had spring up in the past. It is only growing inside crevices in the rockwork of 1 rock.

The only other thing I could think of was a weird tunicate, but it didn't look like any I could find online. What do yall think?

 

[\m/reefsnmetal\m/]

I say sponge. I have yellow sponge just like that in my tank.