Weird feather duster like worm?

[Calappidae]

I can't get a picture it's really tiny.. but there's this strange worm living in my colony of zoanthids. It looks like a combination of a eunice and feather duster.. it's pops in and out (the whole body) and then it opens up it's feather duster like crown/aiptasia like face. It's body is smooth with no visible legs/bristles.

Any leads as to what that could possibly be? It kinda looks like a Sipunculida/peanut worm when I try to look it up, but there is alot less "feathers" on it's crown than those and it's never curled up. It's definitly not a feather duster or spaghetti worm.

 

[Sugar Magnolia]

It could be a small rock-dwelling cucumber.

 

[Calappidae]

It could be a small rock-dwelling cucumber.

It actually looks alot like a medusa worm. I've had it in the same spot for a couple months though.

Its extends, and retracts like a turtle's neck almost. The crown sinks in, then the next segment sinks into the next segment, etc.