If one is about to explain fluorescent and bioluminescent proteins the jellyfish Aequorea victoria is an outstanding example of an organism expressing both.
Aequorea victoria emits light upon mechanical stimulation. The mechanical stimulus triggers the release of the second messenger Ca2+, which in turn binds to and activates the photoprotein aequorin. If activated aequorin generates blue light at 470 nm by an enzymatically catalysed chemical reaction. This process is an example of a chemiluminescent reaction, which is called bioluminescence when occurring in a living cell or an organism.
But in vivo the light emitted by Aequorea victoria is green not blue because the blue wavelengths are directly absorbed by the green fluorescent protein (GFP) and re-emitted at 508nm. The later process is an example for a fluorescence phenomenon. Aequorin is a bioluminescent protein, GFP a fluorescent protein. In light microscopy aequorin has proven useful as an ion sensing dye, permitting the visualisation and measurement of intracellular Ca2+ fluctuations. In combination with molecular biological techniques GFP became an invaluable tool in cell biology (see 'Green Fluorescent Protein').