Is this a baby sponge?

[LardLad]

I thought this was blue/black algae at first. It requires a knife to get it off. My LFS says it is a sponge. Any thoughts?

 

[LardLad]

Another angle.

 

[El_Guapo13]

Are you talking about the blackish looking stuff, or the baby mushroom?

 

[MTBake]

Looks like a type of sponge to me. Not sure on what type though.

 

[El_Guapo13]

How does it compare to this sponge (this is the closest thing I have seen so far to what is in the pic you gave. Not sure on the exact species though)?

 

[LardLad]

Are you talking about the blackish looking stuff, or the baby mushroom?

Yep. The blue/black mass.