Critter ID please

[Alan_J_MN]

I have a zoa frag that's been in the tank about a month. I dipped before introducing it to the tank along with other frags. Nothing came off. In the last week I could see crud building up at one end of the colony. Today the encrustation was larger, so I pulled it out and scraped of quite a bit of the crud. Beneath it was a small calcareous tube.. (you know what I'm thinking!).
I dipped the frag.. and this came out. Maybe just under 1/2". What is it?

 

[Crabs McJones]

Looks like a common bristleworm. Great clean up crew member, just don't try to give it a hug

 

[fishguy242]

bristle worm

 

[SniffanyB]

Bristle worm for sure. They can get pretty big as well from what I've read

 

[Alan_J_MN]

Thanks. I thought it was a bristle worm but didn't want to influence any answers. AFAIK they don't bother healthy zoas, so I suspect something else was causing the crud build up.