What the heck is this?

[deskjockey]

I recently purchased some tonga mushrooms and this was on the LR. It appears to have some sort of sweeper tentacles but they dont seem to harm the mushrooms. When it was first placed in the tank it was almost smooth now it has spike looking things coming out of it! I thought sponge at first now Im not so sure :? . Any help would be greatly appreciated.

Thanks
AP

P.S.
Ill try to take a closer pic tonight

 

[LilFishInBigPond]

You're 1st thought was correct, its a sponge. "Sweeper tentacles" are just new growth.