Tube thing is it good or bad

[tazcliff]

I have of these on my live rock & im trying to figure out if there good or bad. The outer tube is hard & mostly clear, about 1mm in diameter & they are 5-10mm long. There is a white inner portion that retracts when you get near them, it looks like a thick piece of thread & does not fan out. Any Ideas as to what they are ? are they good or bad ? in a FOWLR.

 

[Eliahu]

looks like a feather duster

 

[SnowManSnow]

it's just a filter feeder.

it's fine.

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