Thank you for the idea teevee, it has been posted in the gallery:
http://www.canreef.com/photopost/sho...php?photo=1315
The worm died last night, it got stuck on the filter intake tube. But I found another big one that looks just like the one in the picture, and this morning I counted 12 little worms coming out of holes in the rock. I have no idea what to do about them, there're popping up all over my tank!