Anenome? Sponge? It moves i think?

[Dh0505]

Anyone know what these are? There dotted all around my pipework and back of the tank. Its a fish only setup.

I have a feeling they move as i got rid of one that was on a pot a few weeks ago.
It was one top of the pot then on the rim. I thought it might have been a small nem or somthing. I got rid of that anyways.
Then a few weeks later i see all those lol.

 

[Hogan]

It's a pineapple sponge. Harmless

 

[MTBake]

Pineapple sponges.

 

[Mike N]

It's a pineapple sponge. Harmless

+1
They like very low flow areas