Small 'feather dusters' growing in live rock?

[DKoKoMan]

That being said I currently have 3 feather dusters on my reef tank. Two are Hawaiian feather dusters and one came on a piece of live rock. The others I added myself as my wife enjoys the different colours present on the fan. They are pretty neat as I thought 2 of them died, however the worm just left the tube and setup shop on the sand in a new location. Sometimes they will move if they are being bothered or lose their crown if being nipped at. You will often notice the crown missing and a couple days to a week a smaller crown has been formed. A lot of people will find these as "hitchhikers" on live rock. In my experience they have not caused for any concern.