Help!!! (Follow up)

Original Post: I recently purchased about 60 lbs of live rock and discovered a tentacle hanging off of one of the pieces. It was about 8-10" long. Any idea what it is and if I need to be concerned?

Follow up: Whatever it is (I tried downloading a picture and kept failing), there is a long mucus looking trail in the tank in the exact location where the tentacle hung from last night. I hope this helps in identifying this and thanks to everyone for their previous comments.

 

Tentacle like octopus?

Tentacle like brittle star?

You have my attention, I love a mystery.

 

It looks like a piece of pipe cleaner. Long, thin, straight, with bristles. There is only one tentacle, pinkish-beige in color. Comes out once the T5's turn off. It doesn't move when it is out. It just kind of hangs there. I can't see where it is attached to the rock because it is on the backside of the rock. The mucus film it produced hangs there as well.

 

Bristle worm! Harmless detritus eater, great member of a cuc. Will give a nasty sting if touched.