I can attest to the arrow crab eliminating them from your tank. I had many of the regular pink and black bristle worms, probably the ones you have, and that arrow crab ate every one. I was actually surprised to see them again when I got rid of the crab. Now they are back up to good numbers. I think they're good scavengers and they only eat dead material in my tank, so let them live.
As for coral munchers, I have those too. I have these very strange worms that live in a large rock that is half covered with pink star polyps. Nightly they stick their bodies out of thier holes and munch the the coral. I don't worry about it because they have been there for months and the coral grows faster than they can eat it, so I chose to let them be. The don't look like regular worms though...they are silverish with red irridecent reflections, spikes on the head with a large unicorn like central spike, and two eyes (or false eye spots) that shine red ina flashlight. Very illusive; I can just catch a glimps of them before they hide and it took months of looking at the tank at night before I even noticed them.