@koko & @Arctic Mama
I finally got around to catching one of the suspected detritus worms and popped it under the microscope.
Not the best videos, but you may be able to identify it.
The first is the original video I took after catching one of them, the others were taken yesterday.
As an aside, I also did a scrape on Piggy yesterday - I didn't find squat parasite-wise. I'm going to have another go, as I'm pretty sure I should