Growth on Mushroom? Pic I.D.?

[TomToro]

This thing has been growing on this mushroom for months. Anybody know what it is and is it a specific type of mushroom that grows these green things?
Thanks,
Tom

Here's a far away shot so you can I.D. the type of mushroom.

 

[Paul Davies]

have you a bubble coral in the tank anywhere ?

 

[TomToro]

Yes, but it's at the other end of the tank.

 

[Mishap]

Your bubble could have spawned at some point, definitely interesting looking.

 

[Paul Davies]

my first thoughts, thats why i asked.

looks indentical to a bubble head.

 

[greenbean36191]

Looks like just a distended tentacle to me.