How do the light-sensitive organs of lancelets detect changes in light?

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Lancelets, which belong to the subphylum cephalochordate, possess small, eyelike organs located within their nerve cord. These simple sensory structures function by detecting the direction of light and changes in its intensity. Unlike the complex eyes found in many other animals, these organs are integrated directly into the nerve cord, which features only a slight swelling at the front rather than a true brain.1