Pyrocystis fusiformis is a non-motile, tropical, epipelagic, marine dinoflagellate (flagellate microorganisms), reaching lengths of up to 1 mm. They are especially interesting to many because of their bioluminescent nature which is displayed when P. fusiformis is disturbed or agitated. In the 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.