[Organization of the parenchymula of the endemic Baikal sponge Swartschewskia papyracea (Dyb)].

The larva of the endemic Baikal sponge Swartschewskia papyracea freely swimming in water is a parenchymula which contains all main types of cells peculiar for the definitive sponge. Ultrastructure of these cells is described. Flagellar cells of the larva form a continuous layer with signs of polarity in distribution of organoids and inclusions specific for epithelial cells. Early specialization of collencytes secures, already at the larval stage, synthesis of a specific protein--collagen. Cytoplasm of blastomere-like nucleolar amoebocytes is overloaded with yolky inclusions at various stages of digestion. A developed Golgi complex is characteristic for this type of cells. Amoeboid cells with peculiar inclusions limited with a membrane and filled with a fine fibrillar material having central electron opaque granules are revealed.