The biggest animal known to glow its own light isn't a jellyfish, it's a shark
In 2021, researchers studying deep-sea sharks off New Zealand confirmed the kitefin shark, which can grow over five feet long, produces its own blue-green light from special cells across its skin, making it the largest known bioluminescent vertebrate. Living 650 to 1,000 metres down in near-total darkness, it may use the faint glow on its belly to cancel out its silhouette and hide from predators lurking below.