Weird feathery threads from a tiny creature? o_O

[An_Enemy]

My partner and I have just bought home a live rock for our first reef aquarium and she spotted these tiny threads coming from it.

The creature seems to have a tiny, soft body with two feathered threads attached to little bumps. The creature is about 5mm and the fine threads reach around 6 inches! I can't tell for sure, but the threads might be extending/retracting to the body.

Any ideas what this bizzare little dude might be?

 

[reef lover]

Comb jellies....never had any survive long term.

 

[An_Enemy]

Comb jellies....never had any survive long term.

Thanks for the ID! Shame it won't last long, but a quick search says their entire life cycle is only a few months as it is.