Sponges (phylum Porifera) are phylogenetically ancient Metazoa that use silicon to form their skeletons. The process of biomineralization in sponges is one of the important problems being examined in the field of research focused on sponge biology. Primmorph cell culture is a convenient model for studying spiculogenesis. The aim of the present work was to produce a long-term primmorph culture from the freshwater Baikal sponge Lubomirskia baikalensis (class Demospongiae, order Haplosclerida and family Lubomirskiidae) in both natural Baikal water and artificial Baikal water to study the influence of silicate concentration on formation and growth of spicules in primmorphs. Silicate concentration plays an important role in formation and growth of spicules, as well as overabundance of silica leads to destruction of cell culture primmorphs. We also found that the composition of chemical elements (Si, O, C, and Na) varied along the length of growing spicules at cultivation in different media. The long-term culture of Baikal sponge primmorphs will be necessary for further investigations, and this system may serve as a powerful in vitro model to study spiculogenesis in Baikal siliceous sponges during the early stages of intracellular spicule formation to identify genes that affect biomineralization.