Feather duster with parasite?

[Sansan]

Hi, I'm new to the hobby, I have a 90 gallons tank with a 30 gallons sump, running since this March. In August I got a feather duster, and had to put it back in place twice. The second time, it looked like a piece of dried-up tail was hanging out of the tube. Today, I noticed the end of the tubes was out of the sand again, and looked a lot shorter... And with lots more of flesh exposed. And the end looks... parasited. I have these wierd circles on my rocks, but one is growING out of my feather duster!
So, what is it, and what do I do?
Ps how can I insert a picture in this post?

I did put it as an avatar..

 

[Sansan]

Found how to upload...

 

[Tahoe61]

Those actually look like hitch hiking corals or pest anemones called Majano.

 

[Sansan]

The animal actually has a long, orangey body that extends out like a tongue, with the crown of bubble-tipped tentacles at the top. A friend suggested peanut worm, but the ones I have don't quite look like that and don't actually leave their hole.
But the main question is, what do I do? I have some aiptisia-X, should I spray it on the feather duster's tail to smother the other thing, or cut off the tail? Or just let it be?