New creature. What is it?

[reefing.on.reefer]

I’ve been seeing these red fan shaped creatures popping out of my rock the last few day
they appear to have little tunnels that they pop they’re heads out. Can anyone name this and let me know if it’s a threat to the reef

 

[homer1475]

Tube worm

Filter feeder and a great part of your CUC.

 

[Katrina71]

Feather duster

 

[notsobigtime]

They appear to be feather dusters. Common hitchhikers. I've got a couple snails with them in their shells.