I see these in my fresh water samples sometimes. It looks like a cell or maybe a cyst of some water organism? It's a time lapse and the "cell" actually grows slowly and there seems to be chrloplast slowly moving inside as well. Would love to know what these are.
https://youtube.com/shorts/kkCk-NG66K0?feature=share
Side note you may notice the algae directly north of the "cell" expands a chamber holding chloroplast. Looked really cool.