Originally Posted by specialk
That looks like a hydroid to me but I may be way off. Waiting to see what steve-s says.
It is possible but without being able to see both ends, hard to confirm. If you look closley, the "critter" seems to be segmented which would suggest a worm. I am thinking more towards a species of Phyllodocida spp.
not compeletly sure though. If a hydroid or predaceous worm, it should be removed carefully or it could spread.
Easiest way would be sacrificing a pair of new stockings. Cut a small swatch and place a small piece of shrimp or other meaty raw seafood in it. Loosely tie it with string and place it as near to the coral as possible. If a worm, it will become entangled in the nylon and can be easily removed. You will get a few other stragglers but nothing to be concerned about. If possible, place the "trap" above substrate level.