The work was aimed at performing long-term cultivation of primmorphs in vitro from freshwater sponge Lubomirskia baikalensis (Pallas 1776), collected from Lake Baikal, obtaining its long-term primmorph culture in both natural (NBW) and artificial (ABW) Baikal water and at identifying the impact of different environmental factors on formation and growth of primmorphs. The first fine aggregates of L. baikalensis are formed in vitro 10-15 min after dissociation of sponge cells. Epithelization of aggregates begins 4 h later after the dissociation. Young primmorphs are formed 1 or 2 days later. The surface of primmorphs is covered with a layer of exopinacocytes. The primmorphs remain viable for more than 10 months at 3-6 °C. Over 50% of primmorphs in NBW and 25% in ABW are attached to the substrate and grow like adult sponges. Thus, the long-term primmorph cultivation in vitro allows the creation of a controlled live model system under experimental conditions. The results of this work will allow the creation of a cell culture collection of Baikal freshwater sponges for studying morphogenesis of primmorphs during cultivation at different stages and transdifferentiation of their cells, physiological functions of sponge cells, processes of spiculogenesis, identification of proteins involved in biomineralization process, decoding of their genes, as well as a spectrum of secondary metabolites.