Mostly likely yes its bad. I'd get it out with a pair of twizzers if u can. Not sure what kind it is, but I always thought the bigger they were, the worse off they r lol
I believe I just read something recently about using a nylon stocking with food, something like mysis i presume, in the end. The worm crawls in but has difficulty getting out. I've never personally tried this, just read about it in another post.
also....
Here is a video from Indo Pacific Sea Farms talking about the difference between good worms and bad.
You can take some bridal veil and place food in the middle and wrap it loosely around it. When it goes after the food he'll get tangled up. Then just lift him out
Lol, I nearly had him! He's so long he was feeding off it and his body was still in the live rock. Tried to grab him with plastic pinchers but he wriggled out! I'm gutted. He was in the bottle within 20min of putting it in the tank.
Looks like a eucinid rock worm kill it if you can but they suck to get out. Drill a hole in a peice of LR and stuff some mysis in it, if you can get him to stick his head in the hole hes as good as dead. They have great eye sight mine could see me through the tank. Hell eat your inverts too if he can so keep him fed till its gone haha