Mag. 400x
Perhaps T. spinigera as seen here http://protist.i.hosei.ac.jp/PDB/Images/Heterokontophyta/Tetraedriella/sp_1b.html. The composite picture (the last image) were all taken of the same specimen as it tumbled in response to disturbances in the medium (rotifers careening about).
A pond edge water sample (freshwater) was taken on 9/17/2021 using a 10 micron dip net to enrich for microorganisms.

Mag. 400x
Fungal spore? Saw only 1 in a 24x50mm field.
A shoreline water sample was taken on 8/26/2021 from a cove off the Thames River estuary (New London county, CT - brackish) using a 10 micron dip net to enrich for microorganisms.

Mag. 400x
Like a sleeve green Oreo cookies! Discoid cells appear to be loose within the trichome cell wall, most cells packed perpendicular to to the long axis of the strand, providing a lateral view of the cells. Occasionally, however, cells are tipped giving a partial or full apical view. What is this, @roman_romanov!? Stigonema?
A shoreline water sample was taken on 8/21/2021 from a cove off the Thames River estuary (New London county, CT - brackish) using a 10 micron dip net to enrich for microorganisms.

Mag. 400x
As seen here https://planktonnet.awi.de/index.php?contenttype=image_details&itemid=64874#content. According to AlgaeBase, two species are found in marine and estuarine environments, M. sabulicola and M. marina, and are candidates for the ID of the current specimen. https://www.algaebase.org/search/genus/detail/?genus_id=44298&-session=abv4:AC1F249F13c7d2CB6AQv2999E6DA
A shoreline water sample was taken on 8/21/2021 from a cove off the Thames River estuary (New London county, CT - brackish) using a 10 micron dip net to enrich for microorganisms.

A juvenile hatched while keeping a wild caught adult specimen for some days. Possibly https://www.inaturalist.org/observations/89532507 or https://www.inaturalist.org/observations/89533589.
Some movies focussing through structures are also available.

Mag. 400x
Estuary shoreline sample (brackish). These loricae were relatively common (saw ~6 after scanning a 24x50mm field on one slide). Initially thought these were the loricae from a lobose aomeba, but found images of the peritrich, Pyxicola pusilla in a journal article that correspond very well. Perhaps the 2 specimens I show here are from a closely related genus or specie. https://www.researchgate.net/publication/345494459_Novel_contributions_to_the_peritrich_family_Vaginicolidae_Protista_Ciliophora_with_morphological_and_phylogenetic_analyses_of_poorly_known_species_of_Pyxicola_Cothurnia_and_Vaginicola/figures
A shoreline water sample was taken on 7/27/2021 from the Thames River estuary (New London county, CT) using a 10 micron dip net to enrich for microorganisms.

traits fit to Ophryoglena flava; which is not listed in iNaturalist`s database. More images here:
https://www.plingfactory.de/Science/Atlas/KennkartenProtista/01e-protista/e-Ciliata/e-source/Ophryoglena%20flava.html

Mag. 400x
Photos 1 - 3 are apical views of a semi-cell. The 4th photo is a lateral view of a nearly empty specimen.
A water sample was taken on 7/7/2021 using a 10 micron dip net to enrich for microorganisms.

Mag. 400x (photo 1 and video)
Mag. 100x (photo 3)
Close inspection reveals 2 flagella per cell, one long and one short (the shorter flagellum looks to be about 1/3 the length of the longer).
A water sample was taken on 6/15/2021 using a 10 micron dip net to enrich for microorganisms.

Mag. 400x
Difficult to resolve (need phase (@bdstaylor !) - Each cell appears to have 3 appendages that seem to form a tripod. These appendages did not move nor did the cell swarm (as Diplophrys did in a colonial setting, see https://www.inaturalist.org/observations/72584434). I'm completely stumped with this one. Ideas Bruce and Roman? @roman_romanov
A water sample was taken on 6/15/2021 using a 10 micron dip net to enrich for microorganisms.

From floating algae mat sample kept sealed indoors under continuous lighting for one year. Scraping from side of the plastic bag.

Photos of different individuals found on same slide. Possibly multiple species, but I think they are at least all the same genus.

Very fast; very cylindrical (reminiscent of a flying can of tomatoes); had to wait until it was tuckered out (about 1hr under the cover glass); It's maniacal travels slowed to a photographable pace. Fun to watch!
A pond-edge water sample was taken on 3/19/2021 using a 10 micron dip net to enrich for microorganisms. Air temp. 46F

Cyanophycée marine (Oscillatoria auct.?), à faible profondeur (-1 m) dans une zone à forte houle.
A, B, C Aspect in situ, sur un rocher ; D Au microscope, vue générale ; E, F (idem) trichomes peu courbés + hormogonies bien droites ; pas de gaine mucilagineuse visible.

Video shows it eating a Culex mosquito larva, other photos taken after it ate. Found on Chara aspera.

I think I will keep this as a pet. It won't ever die of old age, and is a convenient way to get rid of small unwanted invertebrates.