Both beautiful to behold and somewhat mysterious, bioluminescence has arisen a number of times in the history of the life on earth. The exact ingredients can differ slightly, but all bioluminescent creatures glow due to a standard chemical reaction: a molecule called a luciferin is oxidized by an enzyme luciferase, generating a cool light. Animals with this ability use it for a variety of purposes, from misdirecting predators to attracting mates. In the graphic below, designer Eleanor Lutz shows us the amazing diversity of light-generating organisms and their relation to each other on the tree of life.
Graphic courtesy of Eleanor Lutz
The Origins Of Marine Bioluminescence: Turning Oxygen Defence
Mechanisms Into Deep-Sea Communication Tools. The Journal of Experimental Biology 201, 1211–1221 (1998) http://jeb.biologists.org/content/201/8/1211.full.pdf
Haddock, S.H.D.; McDougall, C.M.; Case, J.F. “The Bioluminescence Web Page”. Accessed August 5, 2014. http://biolum.eemb.ucsb.edu/