ID please :)

I posted this in my build thread, but figured it should go here as well.

It's the small rounded thing with holes in the center of the picture.

Can anyone identify this? It's about the size of a dime, and has a center mouth, with other holes around it. I have about 3 or four of them in my tank, and they seem to prefer shaded areas. My best guess is some kind of sponge, but I could be completely wrong.

 

Looks like some type of sponge to me too.

 

Yeah, that's what i'm thinking... it seems to be somewhat hollow inside, but it's pretty hard to tell.

I also just realized that there is another one in that picture to the left. It is a side-view, and that one is about twice as big.

 

I agree. I have the same type of yellow sponges.

 

Might be a tunicate