Help w/ algae or pest ID

[jptrson]

Can anyone ID this, at a glance it looked like an algae, but retracts when touched. In the picture the rock is about golf ball size. It's in a friends tank and he has taken the rock out and scrubbed it, but has come back after a few months. Almost looks like little brown Dandilions?
Thanks

 

[saltycreefer]

Look like hydroids which really suck. Throw it out.

 

[jptrson]

Thats sorta what I thought, but I've never seen any. Like an alien life form to me, but might give me a place to start doing some research. He says his tank is loaded, but I'me not sure how big his tank is or how much rock.
Thanks.