Anyone ID this bubble like growth?

[Mailman17013]

I've noticed this bubble like growth on this Rhodactis mushroom plug. Anybody have an idea what I'm looking at here?

 

[davidcalgary29]

It looks like a type of sponge.

 

[Tcook]

Looks like a sponge

 

[Mailman17013]

It looks like a type of sponge.

Thank you!

 

[Mailman17013]

Looks like a sponge

Thanks for your response. Much appreciated!