You can just take small part and put it sterile dist water, shaking for maybe about 5 min and take a small volume (0.2ml) spread over fungi media and incubate 28 degrees centigrade's for 3 days and watch the growing colonies. These colonies might be fungi

Thank you very much for your answer. Unfortunately, we can't run a culture from these organisms, as we detected them only on SEM (they are rarely found indeed) and haven't any other sample to isolate. So we can only based our work on the SEM pictures, which is rather difficult to confirm this group. Sincerely yours. K Comte

Resolved problem of identification!

Hi everyone, After a lot of research and asking to different experts in microalgae, fungi and bryologist, it seems that these unusual shapes growing on the middle of the mosses are also produced by the mosses herselves, and are some reduced leaves called paraphyllium structures. They can have a large variety of shapes (the bifurcated ends are rarely observed though) and are developed by the mosses to increase the photosynthesis process (that's why they matched strongly under the epi-fluorescence microscope!)  or to survive to the dessication stress. Problem resolved! Thank you all for your answers and for the followers!