Probably S. minus.
Moniliforme nucleus consisting in multiple "spheres"
A long terminal vacuole.
We found it in the freshwater that looks at the beginning of the video.
10X and 20X objectives.
Oblique polarized light.
Panasonic GH4 camera
Video link:
https://www.youtube.com/watch?v=os98IP3krys
Video frame preview:

Regards
carlos