Answer: Enterobius vermicularis (pinworm) male and female adults
The adult worms are easily identified by their prominent lateral alae:
The male and female can be further differentiated by looking at their tails; males have a coiled tail while females have a straight tail.
This case is unusual for a couple of reasons; first, we don't typically see adult pinworms in stool specimens (they are more commonly [and ideally] detected using tape preparations), and second, it is even less common to see male pinworms in clinical specimens. The females are more commonly seen because they are the ones that leave their safe residence in the large intestine/cecum to travel nightly to the perianal folds to lay their eggs. The males typically remain behind. The fact that we see both male and female pinworms in stool makes me wonder if this was a particularly heavy infection.
Thank you again to George from MSKCC for donating this interesting case!