Photographing bdelloid rotifers is sometimes a little bit tricky. Of course there are "easy" ones like Rotaria or some Philodina species, which live in ponds or other between small benthic algae or detritus.
But most of the bdelloid rotifers live in mosses or soil, an environment with little water, where they live in a thin film of water covering the moss leaves or small grains of sand or humus. For identification the view of the corona is essential; but the conditions under which the some rotifers like Macrotrachela or Mniobia show their corona are not the best when observing them with a microscope. It seems that the illumination deters some species from whirling. Some species seem to need some small grains of sand or moss leaves. It took two days for some species before I could see them opening their corona for a minute or so.
If the water evaporates under the cover glass or if the oxygen gets low some bdelloids contract, thus preparing for the state of anabiosis in which they can survive for several months.
These conditions are not the best for photographing, as the thickness of the water film between the rotifer and the cover glass strongly influences the sharpness of the images.
If the specific needs of a bdelloid species requires small grains the use of apochromatic lenses maybe impossible because the distance between animal and coverglass is out of range for the lens.
If the rotifers are light sensitive the use of light-consuming contrasting methods, e.g. differential interference contrast (DIC) may disturb the critter thus contracting.
I would like to thank Nataliia Iakovenko and Aydin Orstan for their unvaluable personal help and support for understanding the biology of bdelloid rotifers.