I've had a problem with Fulgida worms for a few years now, two of them I've gotten rid of, a bit by chance, but there's at least one more I've yet to hunt down.
The first one was kind of dumb luck, it had made itself at home in the active carbon in my fuge. The second one I spotted at night and had left its burrow and crawled in under a frag that was laying loose in the sand bed, and was pretty easy to grab with a pair of tweezers.