Perhaps Ploeotia oblique
It has form of lemon, a small flagellum directed forward and another very long and thick directed backwards.
It has an ingestion organelle, visible as a small 'tube' in the video.
Its body measures about 16um (0.016mm) long
We found it in the heavily polluted freshwater of the Rio de la Plata - Route 1 Km 151,500 Artilleros - Colonia - Uruguay.
100X immersion objective
phase contrast and oblique ligh
Panasonic GH3 camera
Video link:
https://www.youtube.com/watch?v=atw-sQ1y9bo
Video preview:
Regards
carlos