Answer: not a parasite; most consistent with mushroom spores.
In this case, the spores were noted in the stool of an individual who had consumed morel mushroom spores, and therefore we can be more specific about the identification.
Mushroom spores are a convincing mimic of parasite eggs. They can be differentiated by a few features, however:
1. Their size is smaller than Enterobius vermicularis eggs - one of their closest mimics.
2. Although in the size range for some of the smaller trematode eggs (e.g. Clonorchis, Metagonimus), they lack an operculum.
Again, special thanks to George who donated these images and reminded me that it is now morel mushroom season!