Fig. 7. Rapid contractions (`twitches') occur simultaneously in distinct regions of the choanosome after uptake of inedible ink. (A) Projected area (density of the tissue) was measured as a proxy for the extent of contraction of the tissue; a contraction was observed as a decrease in the area occupied by tissue (a decrease in blackness). (B) The change in projected area of each region shows that two contraction events occur within seconds of each other in Areas I and II of A, 700 µm apart. (Movie 2 in supplementary material.)