Investigating the potential for image forming vision in Strongylocentrotus droebachiensis

Abstract

Sea urchins have no eyes or eyespots, and yet studies have shown that they are capable of photosensitivity and image forming vision. While the mechanisms that underlie this are not yet clear, visual resolutions of urchins can be determined behaviorally by their orientation towards static targets on the edge of circular tanks. I gathered twenty Strongylocentrotus droebachiensis individuals and exposed them to three different isoreflectant stimuli – a uniform control as well as 70° and 38° targets. While there was a slight trend in the direction of the 70° target, the urchins did not show significant orientation towards any of the stimuli. This suggests that if S. droebachiensis are capable of image forming vision, it is very low resolution. Additionally, this study suggests the potential that dark stimuli commonly used to study urchin vision may be less effective at distinguishing between directional photosensitivity and image forming vision than thought.