The "Can of Worms" achievement requires that you "Find the Purple Tootfish". There are a lot of different scenes in this game, and I've yet to find it or any sign of it. In one level there are a bunch of ball-creatures and I've bludgeoned them endlessly producing several purple variants, but I've never received credit for this achievement.
After a little research I found that you need to "catch" each of the worms that appear on fishing hooks, both the individual worms and the "cans" of worms. Once you've done this about 5-6 times, the Purple Tootfish will appear. I don't know if prevents you from completing the acheivement, but I recommend avoiding the non-worm fish hook items. At the least they waste time, and they may prevent you from getting the achievement - especially if you are using director mode.