Tiny Snails/Spirals

[Orca1]

I just noticed I have a bunch of tiny snail looking organisms on the back of my tank. I mean tiny. They're maybe a millimeter across. Unfortunately, I can't get a clear pic due to their size. Looking at them from the outside of the tank, they look like a tiny spiral. They also don't seem to move around much making me think they're not even snails and possibly some kind of tube worm. They also only seem to be in the shaded areas of the tank.

Anyone have any ideas about what they are? Are they something to be concerned about?

Thanks.............E.

 

[DevIouS]

Spirorbid worms?

 

[Orca1]

That's them......100%