In Summary:

• Bioluminescence is a chemical reaction involving the protein luciferin, the enzyme luciferase, and oxygen that occurs to produce light in living organisms.
• The light produced by the organism is used in a multitude of ways, but humans use it for gene marking and studying gene expression.
• The Deep Sea Anglerfish utilizes a symbiotic relationship with light-producing photobacteria in its lure to draw in prey and mates.
• Fireflies use bioluminescence to communicate, attract mates by sending optical signals, and as a defense mechanism.   
  
• Brittle Stars use bioluminescence as a defense mechanism by flashing green lights at their predators.
  
• The Vampire Squid use bioluminescence to disorient predators and attract prey by modulate the size and intensity of photophores.
• The Atolla Jellyfish uses bioluminescence to defend itself against predators.
• Dinoflagellates are unicellular protists that use bioluminescence as a defense mechanism, and are the most common source of bioluminescence on the ocean's surface.