Who do I have hitchhiking on my bubble coral?

[ebeltran]

 

[fishski13]

looks like a tube worm but usually I see them with red or orange heads, so not entirely sure

 

[ISpeakForTheSeas]

Yeah, looks like a feather duster of some variety, possibly a Spirobranchus sp.

Here’s a similar one:

How scared should I be?

www.reef2reef.com

 

[WheatToast]

Spirobranchus cariniferus is a tube worm/feather duster that looks pretty similar to OP's worm:
https://commons.wikimedia.org/wiki/Category:Spirobranchus_cariniferus
https://www.inaturalist.org/taxa/397374-Spirobranchus-cariniferus/browse_photos