Mag. 400x
Small amoeboid organism. Often fan shape, narrow portion trailing, wide portion leading. The leading edge is transparent. Organellar material is concentrated in the trailing portion. This amoeboid looks very similar to images here https://arcella.nl/vannella-sp/. Photos 2 and 3 are for comparison with a larger, pseudopod-baring amoeboid. For a video, see https://youtu.be/yiZ1RHs2vOI.
Bright-field light microscopy; medium-power. In pond.
Telotroch (free-swimming) phase of a peritrich ciliate. Maybe Vorticellidae? Collected from freshwater stream, 400x magnification.
Mag. 400x
Rotifer with spiny lorica. Dead. Foot not visible though the opening in lorica that accommodates the foot is visible. This specimen looks very much like Plationus patulus as seen here https://www.plingfactory.de/Science/Atlas/KennkartenTiere/Rotifers/01RotEng/source/Plationus%20patulus.html.
x400
Playa de Lekeitio - Beach of Lekeitio
Video: https://youtu.be/DmfKQNC4GpE
Mag. 400x
Euglenoid. Relatively unadorned lorica. Exceptionally long anterior flagellum, the length is best appreciated in the videos. In the 2nd video, I think we are viewing the pore through which the flagellum emerges.
Mag. 400x
Small flagellate with a probing "nose". My scope could not resolve the critter cleanly, but it was fun to chase, after it swam into my field of view. (The 2nd image shows the small, inconspicuous, shadowy figure as it appeared in the 400x field.) I could only see it for a short interval before I lost the ability to track it. For fabulous images and video of R. nasuta, see the observations posted by iNatters @crseaquist and @zookanthos: https://www.inaturalist.org/observations?verifiable=true&taxon_id=881489&place_id=97394&preferred_place_id=1&locale=en-US.