I may be wrong but don't think that a feather duster can be harmed by a coral. My mushrooms touch mine all the time along with sweepers from my Galaxea. My LTA has also touched it. They are polychaetes and likely are immune to cnidocysts (stinging cells) from corals. The tentacles of the tube worm are radioles made of chiton or something like this. They are likely derived from the setae of polychaetes.