Congratulations to all of you who got this one correct! This was actually an older case that I had posted back in 2014. I had forgotten that I already posted it! This case comes with an explanatory photo and a fun poem from Blaine Mathison:
While the duodenum is an unusual place to find this worm,
the morphologic features shouldn't cause you to squirm
With lateral alae pointing to the sides
and platymyarian musculature low and wide
a diagnosis of pinworm should be relatively firm!