Whats Growing On My Rock

[iDad]

Can someone help tell me what this is.

The squiggles are growing off the rock and I just am curious as to what it is.

Thanks in Advance Everyone!

 

[kbuser92]

Harmless yard shelled fanworms.

 

[chichimom79]

Spirorbid worms :) Harmless filter feeders.

 

[kbuser92]

So that's what they're actually called.

 

[chichimom79]

Yep, I had them all over my tank when I bought it used. Wanted to know if it was something harmful or not.