That was to put the size of the worms laying the eggs in perspective. You said you saw a large worm? Could that have been it?
"Capillaria species are relatively transparent"
That's from the same publication as the photo. Transparent fits perfectly with this but I'm just not sure what your seeing if it's not the worms. What's making up the clear or yellowish feces?
If not for the microscope I would of had no clue it was this worm infestation which is running rampant in my poor fish intestines.