Not sure whether or not is was single celled or not, but around 1966 my biology teacher too us on a field trip beyond the football field, where there was a pond. We collected samples of the water and some muck, some algae. We went back to class and made slides, and looked under the microscopes. Every desk had one. We were amazed at what we saw. I identified a rotifer, and a hydra, and got an “A”. Made my day.
Both are metazoans (i.e., multicellular creatures).
Regards,
One of my students’ favorite labs was the protozoans under a microscope lab. I had gone to a nearby pond and collected a bunch of water samples. I taught the students how to use depression slides and pipettes to put a drop of pond water onto the depression slides and then put a cover slip over the slide. We saw many fascinating critters. My favorite protozoan was the pretty blue Stentor, a funnel-shaped proto with the larger end ringed with cilia. Occasionally we got to see one species of proto devour another species, which was very interesting.