I found some kind of laong, slimy sack under a stone inside a cold brook in the mountains. At home, under the microscope I saw that really tiny nematoceran lavae were coming out from it - freshly emeged from eggs, I think.
pwalter attached the following image:
It is the larvae of a Chironomidae, Tanypodinae for sure, but I have no idea about the species or even genus. All Chironomidae lay their eggs in a long slimy sac, which they attach to a hard subtrate at one end. They can contain numerous eggs.
Does someone has a scan of Nartshuk E.P. 2003. Key to families of Diptera (Insecta) of the fauna of Russian and adjacent countries. Proceedings of the Zoological Institute Vol. 294: 1-252 for me?
