Tried magnyfying glass - 16x: they are smooth, like nudibranches, and, because I could see them only on the glass, i.e. their bottom only, looks like they have elongated tail, yellow seemingly soft carapace (as stomatella snail) and something white opaque elongated pieces inside, like sclerites for corals. The head is hammer-like, and scraping eating movements as of the snails.
Advanced cameras were not much of help, this is all I could get:
-Tentacles or antennae in the head, top view (at least it seems so):

- same, plus hammer-like head - the photo on the glass, bottom view:

- practically side view:
The largest ot them are 1.5 - 1.75 mm (1/16") long, or 2-2.5 cyclops body length (also clearly visible on the tank glass with 16x magnification. I thought, that cyclops are freshwater species... You know, pear-shaped body, couple of antennae on the head, and 2 longer paddles as a legs).
Also, the one new thing, only couldn't make photo - camera focuses on the bigger background objects: ~3 mm (1/8", or 5 cyclops bodies lengths) long round worm, slim, white, almost transparent, opaque white eggs-like granules inside the abdomen, hammer-like head (but less expressed, comparing to the first, smaller worms or nudis), and at the end of the first 1/3 of the body - tangerine-orange belt around the body, except the belly.
Really like idea of using magnifying glass - so many new things in the tank!