August 8, 2022

Noctiluca scintillans are marine plankton. It was given this name (Latin: noctis 'night' + lucens 'shining') because it looks brilliant at night when it occurs in large numbers, but it appears as a red tide in the daytime. As a red tide-causing organism, the genus name is often written as Noctylca in kana. In the taxonomy of plants, it belongs to the order Dinoflagellate, the class of phytoflagellates in ancient times, and in the phylum Dinoflagellate in recent years, and in the taxonomy of plants, it belongs to the phylum Dinoflagellate. Unlike common dinoflagellates, they do not have chloroplasts and are heterotrophic organisms that exclusively prey on other organisms.

Cell structure

It is very large for a protist, with giant vacuole (or pusulen)-filled cells reaching 1-2 mm in diameter. The shape is roughly spherical, with a single depression. The cytoplasm is concentrated near the hollowed part, and the round part other than that is rather an expanded cell. Threads of protoplasm extend radially from the cytoplasm of the depressed portion, and can be seen to spread around the periphery in a mesh-like manner. A single tentacle extends from the recessed part. In some cases, green algae are retained as symbiotic algae in the cell, but the chloroplasts of the green algae have disappeared, and there is no reflux of photosynthetic products to the host. The cells have tentacles, which they use to prey on other protists and algae. Apart from tentacles, it has two flagella, but they are inconspicuous. In this way, it is a figure that cannot be thought of as a dinoflagellate. In general, dinoflagellates have vertical and horizontal grooves on their bodies, with flagella running backwards in the vertical grooves and lateral flagella along the lateral grooves. In the case of the green clam, the lateral furrow has degenerated to a trace, and the transverse flagellum has almost disappeared. However, the longitudinal groove is located in the central part where the tentacles are located, and the flagellum is also present here. However, these structures are obscured by the swelling of other cells. As a peculiar point, unlike other dinoflagellates, the cell nucleus is not a dinoflagellate nucleus (chromosomes do not aggregate during interphase), but normal eukaryotes, and normal cells have a nuclear phase of 2n. Diphasic cells are characteristic, while uniphasic cells are the most common form of dinoflagellates.


Like other bioluminescence, luminescence is due to the luciferin-luciferase reaction. Yakouchu has the characteristic of glowing when exposed to physical stimulation, so you can see how it shines especially brightly at the beach. It also glows when you throw a stone at the surface of the water where the yakoutu is, create an undertow from a boat, or swim with dolphins.

Relationship with Red Tide

It is a typical red tide-forming species that is common in coastal areas. During outbreaks, it turns seawater into a rusty iron color, and sometimes takes on a dark and poisonous reddish-brown color that is sometimes described as tomato juice. It occurs in large numbers during spring and summer when the water temperature rises, but there is little causal relationship with the concentration of nutrients in the seawater, and the occurrence of red tide in Yakouchu does not necessarily mean eutrophication. They are relatively common, but because they are small in scale and non-toxic, the damage is often not a big deal. Yakouchu is large and light, and is often distributed near the sea surface. As a result, it is easily affected by the wind and can easily blow up in bays and coastal areas. This feature promotes local discoloration of the sea surface and makes the luminescence seen at night strong and beautiful. Luminescence is due to interspersed intracellular lipid granules, but has never been discussed with any adaptive significance, and is said to be a mere metabolite.