Live rock hitch hiker. What is it?

[Pdandy]

This was on a piece of live rock I added to my tank. What is it? It looks like clear spaghetti or something attached to the rock. (on the lower right side)

http://i1199.photobucket.com/albums/aa478/pdandy88/photo12-1_zps60281376.jpg

[saltyair]

type of sponge or tunicates harmless filter feeder

[cloak]

My guess would be a sponge of some sort as well.