Taxis response experiments using the sea urchin Diadema africanum. To assay the object taxis response of D. africanum to dark objects of varying width, experimental trials were conducted in which individuals were placed in a lit arena, surrounded by printed patterns containing a printed visual stimulus (Fig. 1B). The animals' trajectories in relation to the stimulus were tracked and compared for differing stimulus treatments. This video shows a recording of an individual which has moved towards a 69° difference of Gaussians printed stimulus.