Pyrocystis fusiformis is a non-motile, tropical, epipelagic, marine dinoflagellate (flagellate microorganisms), reaching lengths of up to 1 mm. P. fusiformis display bioluminescence when disturbed or agitated. In coastal marine waters, this dinoflagellate causes glowing effects after dark. P. fusiformis was first described in the Proceedings of the Royal Society of London in 1876. Morphology P. fusiformis's name is derived from its tapered or spindle shape. P. fusiformis is non-motile, which is a characteristic of all members of family Pyrocystaceae, which lose their flagellum by the time these organisms are adults. P. fusiformis is considered a large dinoflagellate, with each cell being approximately 970 x 163 µm long and having a spherical diameter of 374 µm. The cell's chloroplasts actually change the cell's shape as they move closer to the cell's wall in daytime and retract towards the nucleus at night.P. fusiformis is autotrophic, deriving their energy from the sun through photosynthesis. P. fusiformis will only photosynthesize during daylight hours and mostly produce bioluminescence during night because of their circadian rhythm which controls both processes. Bioluminescence Bioluminescence occurs when an organism emits light through a chemical reaction with the majority of the world's bioluminescent organisms living in the ocean. The production of bioluminescence by P. fusiformis is thought to be a defense mechanism that startles grazers which would otherwise eat them or to illuminate grazers so that they, in turn may be more visible to their own predators, known as the "Burglar Alarm" theory. In P. fusiformis bright blue light is produced through the reaction of the enzyme luciferase and protein-like compound luciferin in the cell's plasma membrane. Blue is believed to be the most common bioluminescent color produced in the ocean as blue light waves travels the fastest in seawater. The dinoflagellete type of luciferin used in this reaction is one of the four common types of luciferin found in the marine environment, and the genome of P. fusiformis contains shared common origin with other dinoflagellates that contain the luciferase enzyme. In the laboratory, two different types bioluminescent flashes have been observed. One is bright and quick, while the other is dim but longer-lasting. The intensity and duration of these flashes are dependent on the time a cell has to recharge in between emitting light, with recovery periods varying between 15–60 minutes and 6 hours for fatigued cells. Life cycle P. fusiformis has a full life cycle of approximately 5–7