What is this

[roundman]

No picture but will try for one later.
:wow2:
They came with the rock my mushrooms came on. They are a brown tube (appears soft) about an inch long but there have been nothing come out of them (like feather dusters). They don't open on anything they just sit there.

 

[wbholwell]

I think it's a sponge extension. I have the same thing on some of my rocks, and I think it's a method the sponge uses to reproduce (like a runner from grass such as centipede).

Could be wrong, though.