Practice question

Eyespots or optic cushions located at terminal ends of each sea star arm consist of cluster of photoreceptor cells underlined by pigmented supportive cells, lacking lens, cornea or image-forming optics. Functionally they discriminate light intensity gradients, enabling detection of shadows, approaching predators and orientation toward crevices for phototactic escape, not detailed image formation or color discrimination like arthropod compound eyes or vertebrate camera eyes. Photoreceptive capability coordinates diurnal activity, spawning synchronization and arm withdrawal reflexes. Simple ocellar arrangement exemplifies basic deuterostome photoreception adapted for slow benthic locomotion rather than acute vision.