Phalloidin-stained tissue in control vs. actin RNAi-treated Tethya wilhelma. Confocal laser scanning microscopy images of Alexa 488 phalloidin conjugate-stained whole mount preparations of T. wilhelma. A, D and F. Control treated sponges. B and E. Actin RNAi treated sponges 33 hours after initial feeding (see feeding scheme in Figure 3). C. Actin RNAi treated sponge tissues 57 hours after initial feeding. A - C. Exopinacoderm layers showing pinacocytes. Insets display details of the main image. Arrowheads show Actin ripples at the cell surface as parts of the pinacocyte Actin network. Note: due to slight hypoosmotic fixative in order to avoid cell shrinking, the sponges are slightly inflated during fixation, forming small artifactual gaps between pinacocytes due to their extremely thin contact zones between the pinacocytes. This slight artifact is systemic in all samples and does not interfere with the characters important in the context (see Additional File 1, Figure S11 for more details). D. Three detail images of bipolar (moving) mesohyle cells (arrowheads) in control sponges. E - F. Multipolar cells (arrowheads): hypertrophic, large cells in RNAi-treated sponges (E) and normal multipolar cells in control sponges (F).