Looks like it could be a free living caddis like a Rhyacophila species. It's strange how a small helgrammite can be so similar to a free living caddis. Maybe someone out there with some more entymological knowledge than I could post a method that could be used to distinguish the two species. The free living caddis are little predators too. If you do a Google search on Rhyacophils caddis, you will find alot of information and pictures that look alot like your mystery bug.