Marine dinoflagellates at night can emit blue light by bioluminescence, a process also called "the phosphorescence of the seas". Light production in these single celled organisms is produced by small structures in the cytoplasm called scintillons. Among bioluminescent organisms, only dinoflagellates have scintillons. In the dinoflagellates, the biochemical reaction that produces light involves a luciferase-catalysed oxidation of a linear tetrapyrrole called luciferin. The dinoflagellate Lingulodinium polyedra (previously called Gonyaulax polyedra) also contains a second protein called luciferin binding protein (LBP) that has been proposed to protect luciferin from non-luminescent oxidation. Luciferin is released from LBP by a decrease in pH, and the same decreased pH also activates the luciferase. Light production in the dinoflagellates occurs in bioluminescent organelles called scintillons and can be stimulated by agitation of the surrounding seawater.