ID Please Worm ?

[Shiandy]

I spotted this rather strange looking critter, is sends out a huge sweeper tenticle 12" long (assume to feed) looks like a feather, I'm assuming its some kind of worm. Actual critter is pink, but very hard to see at its living on my sea whip, and hides extremely well.

Harmful to my inhabitants ??

 

[KAiNE]

Its a comb jelly.
http://reefcentral.com/forums/showthread.php?s=&threadid=695167

 

[Travis L. Stevens]

That's the one. Here is a clearer picture for you.