worm inside casing?

[New2reef]

Hi! this appeared 2 weeks ago. it is growing and sucks in brine shrimp. the end of the white tube is translucent and fuzzy. is there a worm inside? friend or foe? Thanks for any advice -- still climbing the learning curve

 

[oldrey]

It looks to me some sort of feather duster, if so all is good. Leave it be.