Answer: Acanthamoeba sp. cysts and trophozoite.
Wow, I really enjoyed reading the comments on this case! If you haven't already, I encourage you all to ready the holiday tale of Ascaris suum (a.k.a. Ascaris lumbricoides) by Old One. The story confirmed my suspicions of why we see so many cases of human ascariasis in patients from the Midwestern United States who haven't traveled internationally. The pigs are loaded with them!
The comments also nicely describe the differences between the cysts and trophozoites of the free-living amebae that most commonly cause human disease: Acanthamoeba species, Balamuthia mandrillaris, and Naegleria fowleri. Therefore I won't describe them further here. However I will show you some of the main discernible features from the transmission electron micrographic images in this case: