Answer: Dientamoeba fragilis
This organism has an overall structure like an amoeba, but has an internalized flagellum, and is therefore most accurately characterized as a flagellate. It is sometimes referred to as an amoeboflagellate. As nicely described by Florida Fan, D. fragilis has a characteristic nucleus with 'fragmented' appearing chromatin. It commonly has 2 nuclei, but may also have 1, as seen in some of the organisms in this case.