Some bioluminescent species get really cranky when you disturb them. Tomopteris, a tiny marine worm, erupts into a shower of angry sparks and unloads its eggs into the water before rapidly undulating away. What is unusual about this worm is that the sparks it shoots from its paddle-shaped swimming legs are golden yellow in color and not blue, like practically every other bioluminescent organism.

Other marine worms are thought to release glowing blue particles into the water to make themselves look less tasty to hungry predators. Few deep-living species have the ability to detect yellow light, which, because it has a higher wavelength, gets absorbed in the shallow surface waters, so it is unclear why Tomopteris uses it. For the moment, researchers are still trying to suss out the chemistry of the yellow luminescence, which may yield some clues about its unique function.