I cant really tell from the picture, but the general knowledge is, if you have shrimp only tank, without any fish to eat this, the water will develop the usual things you will find in the outside waters, zooplankton, daphnias and other critters. I will try to find the article where I have seen it, many are not harmful, some will be tiny worms from detritus (also not harmful). I also have a shrimp only tank and to avoid this, I have Utricularia gibba, the smallest of "meat-eating" aquatic plants, that is supposed to deal with these small critters and is too small to capture even a newborn shrimp.
However, I have had the shrimp tank only for 3 months and am barely getting first batch of babies, so no real results yet, and I saw something microscopic hop around in my tank too, so who knows.