Help critter question

[Lee's Fragtacular Corals]

Last night i fed my chalices and i went back to check on them and there was a big gray bristle worm on top of one of my chalices. I tried catching it but it was attached to the rock. A little bit later it was back on the chalice. This morning when i woke up there were to two dead spots where the bristle worm was. Has anyone ever experienced this before? Also, how do you catch a bristle worm that is still attached to the rock?

 

[Lee's Fragtacular Corals]

Here's a picture.