Hypotrich ciliates can be difficult to identify, but the common species
Tachysoma pellionellum is easier than most, because of its distinctive size and shape (the cell is <100 μm, narrow, often with a distinct lateral bulge in the vicinity of the contractile vacuole, at mid-body), combined with its very long, trailing transverse cirri (usually splayed out and rather stiff). It resembles another common ciliate,
Holosticha pullaster, but the latter has its contractile vacuole in the posterior third of the cell (a very unusual position for hypotrichs).
T. pellionellum also has long dorsal cilia, which extend around the margin of the cell, as a series of regularly-spaced fine bristles. See pp. 433 ff., here:
https://www.researchgate.net/publicatio ... ypotrichia A search in Google Images should turn up some images and videos (but most have not been identified by experts, so be wary). You can also find images of the critter on iNaturalist:
https://www.inaturalist.org/home. Older sources may use the name
Oxytricha pellionella, and it also sometimes appears under the name
Tachysoma pellionella.
The ciliate we see at 2:54 in your video has trailing transverse cirri, and CV is at mid-body (with a distinct swelling in that region). We don't see dorsal cilia (darkfield looks pretty, but not very good for ciliate identification!), but I am pretty sure the critter in that part of the video is
T. pellionellum. The one that appears at 6:25 looks quite different, and I can't say much about it, except that it is probably an oxytrichid, and not a urostyloid.
