Long green worm with ribbon end ID?


Reefing newb
Noticed by chance once I’d turned the room lights on in the night, at first thought a piece of string had fallen in some how then saw it move and retract into the rock.
Gets very long (up to 5/6” from what iv seen) maybe longer and hangs down the side of the rock in the night with a double forked ribbon type end.
Just want to make sure it’s not harmful to anything else as the ribbon end looked a bit like a lure.
Photos from a video of it extended then retracting into the rock.


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Looks like it could be a vermetid snail, although it's tough to tell from the pictures shown. Maybe even a spionid worm?

In any case, I'd assume those "tentacles" are searching for food. I wouldn't expect them to be harmful, but I'd keep a close eye on it and the other things in your tank just to be sure.