Sponges are a group of primitive animals that are of particular interest in terms of the evolutionary theory. Molecular and phylogenic studies have revealed the common origin of sponges and Metazoa and the relation- ship of Metazoa with Choanoflagellata. The comparative studies of the morphology allowed one to recon- struct the structure of ancestors common for Metazoa and Choanoflagellata, as well as for Porifera and other Metazoa. For this purpose, a comparative analysis of phylogenically informative structures, such as kinetid is needed. This article presents the data on the structure of choanocytes' kinetid in Haliclona sp., which was in- vestigated for the first time. The reconstruction of kinetid based on ultrathin serial sections shows that it lacks accessory centriole; it has fibrillar roots despite the basal position of nucleus; two-three triplets of kinetosome are longer than the others; bundles of lateral microtubules arise from fibrillar roots and reach the cytoplasmic membrane in the region of intercellular contact. The studies of the kinetid in few investigated representatives of Demospongiae showed a compatibility of the data on ultrastructure and molecular phylogeny.