I didn't get that out of the link. The dropping its crown is just something that happens from time to time and not to worry as they grow back.
As far as reproducing, it seems there are 2 ways depending on the species. One is the worm break its butt off and the mother grows a new butt and the butt grows a head/feather. The other way is spawning, releasing stuff into the water.
What I got out of that is, it is possible to have 2 featherdusters next to each other and if a spawning event happens they can reproduce. Or the other way is the butt end breaks off and the worm moves a little in the sand and replants itself and the broken off part left behind will grown into a whole new featherduster.