Cilia are found on the epithelia lining the osculum . a. The sponge Ephydatia muelleri in the lake, and grown in the lab viewed from the side (upper inset) and from above (lower inset). The oscula (white arrows) extend upwards from the body. b, c, Scanning electron micrographs show cilia arise from the middle of each cell along the entire length of the inside of the osculum; b the lining of the osculum with cilia on each cell (inset shows an osculum removed from the sponge and sliced in half longitudinally); c, two cilia arise from each cell. d, e, Cilia in the oscula labeled with antibodies to acetylated α-tubulin (green), nuclei with Hoechst (blue, n), actin with phalloidin (red). f. A 3D surface rendering illustrates how the cilia arise just above the nucleus of the cell. Scale bars a 5 mm; inset 1 mm; b 20 μm; inset 100 μm c, 1 μm d, 20 μm e, f 5 μm.