The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Yes, the pic is a little too fuzzy for exact type identification but the Antennae make it appear more a nudibranch then a bristleworm. Some Nudis are good at eating things like Aptasia and algaes while others are coral eaters so I would get a positive ID before you remove it. Maybe for now, get a net breeder and keep it in there to prevent you from losing it in the tank before you get the positive ID ( and you can get a clearer pic of it as well. )
I've just pulled another two out, all 3 have been on the glass and I can't spot any in/on my corals. I'm struggling to get a good picture as there so small!
There are a number of sites online that have pics of Nudibranchs. Google some of those and look through the pics to see which more closely resembles what you have if you can't get a good pic to post.