I would look at Mallomonas. The ellispoidal/elongate cell in the center of the last image is the best example for this. I get a sense of the scales in all the images, and I suspect that they dropped their spines as a result of Lugols .
Kind of Chrysophyte call. Might be lost by Uroglena or might be Ochromonas. In case you see ingested algae (e.g. Centrales) inside, most probably Ochromonas. But it is so difficult with these creatures. We mostly count them as "other Chrysophytes" and if we are lucky we can identify (but only from a living sample)