Noctiluca scintillans

Noctiluca scintillans, is the sea sparkle. It is a free-living marine-dwelling species of dinoflagellate. 
It shows bioluminescence when disturbed: this produces a "milky seas effect". The bioluminescence is produced in the cytoplasm of this single-celled protist. It is done by a luciferin-luciferase reaction in thousands of spherical organelles, called scintillons. Nonluminescent populations in the genus "Noctiluca" lack these scintillons.
"Noctiluca" is a heterotroph (non-photosynthetic) that engulfs by phagocytosis. They eat plankton, diatoms, other dinoflagellates, fish eggs and bacteria. The diatom "Thalassiosira" is known as a favourite food source of "Noctiluca".
"N. scintillans" also takes in tiny phytoplankton which live as endosymbionts. They do photosynthesis for their larger host. Diatoms are often found in the vacuoles (internal membrane-bound storage compartments) of "Noctiluca". The green non-feeding symbionts can grow photoautotrophically for generations.