Bristleworm stealing food from open brain

[trilinearmipmap]

Yesterday I fed my open brain some mysis, a large (at least 6") bristleworm came out from a nearby rock, climbed over the open brain, and stole the mysis.

I have left my bristleworms alone because they are supposed to be harmless but I understand without feeding the brain (Trachyphyllia sp.) will die.

Anyway I'm considering trapping the bristleworm but want to hear some input on this, I don't want to move the open brain.