The Dinoflagellates (from Ancient Greek δῖνος (dînos) 'whirling' and Latin flagellum 'whip, scourge'), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata[5] and are usually considered protists.

[13] In 1753, the first modern dinoflagellates were described by Henry Baker as "Animalcules which cause the Sparkling Light in Sea Water",[14] and named by Otto Friedrich Müller in 1773.

In the 1830s, the German microscopist Christian Gottfried Ehrenberg examined many water and plankton samples and proposed several dinoflagellate genera that are still used today including Peridinium, Prorocentrum, and Dinophysis.

[18][19][20] The transverse flagellum is a wavy ribbon in which only the outer edge undulates from base to tip, due to the action of the axoneme which runs along it.

The flagella lie in surface grooves: the transverse one in the cingulum and the longitudinal one in the sulcus, although its distal portion projects freely behind the cell.

All the same, the dinoflagellate cell consists of the more common organelles such as rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, lipid and starch grains, and food vacuoles.

In place of histones, dinoflagellate nuclei contain a novel, dominant family of nuclear proteins that appear to be of viral origin, thus are called Dinoflagellate viral nucleoproteins (DVNPs) which are highly basic, bind DNA with similar affinity to histones, and occur in multiple posttranslationally modified forms.

[31] Dinoflagellate nuclei remain condensed throughout interphase rather than just during mitosis, which is closed and involves a uniquely extranuclear mitotic spindle.

[2] English-language taxonomic monographs covering large numbers of species are published for the Gulf of Mexico,[45] the Indian Ocean,[46] the British Isles,[47] the Mediterranean[48] and the North Sea.

However, endosymbiontic Zooxanthellae inhabit a great number of other invertebrates and protists, for example many sea anemones, jellyfish, nudibranchs, the giant clam Tridacna, and several species of radiolarians and foraminiferans.

In several Protoperidinium spp., e.g. P. conicum, a large feeding veil—a pseudopod called the pallium—is extruded to capture prey which is subsequently digested extracellularly (= pallium-feeding).

A unique pigment in dinoflagellates is peridinin, a specialized carotenoid that plays a key role in light harvesting and energy transfer to chlorophyll a.

[75] Peridinin is highly efficient in capturing blue light, which penetrates deeper into the water column, giving many dinoflagellates a competitive advantage in stratified or turbid environments.

[76] Additionally, dinoflagellates contain other carotenoids such as diadinoxanthin and dinoxanthin, which play important roles in photoprotection by dissipating excess light energy and preventing oxidative stress under high irradiance.

Under such circumstances, they can produce toxins (generally called dinotoxins) in quantities capable of killing fish and accumulating in filter feeders such as shellfish, which in turn may be passed on to people who eat them.

Bluish flickers visible in ocean water at night often come from blooms of bioluminescent dinoflagellates, which emit short flashes of light when disturbed.

Although the resulting red waves are an interesting visual phenomenon, they contain toxins that not only affect all marine life in the ocean, but the people who consume them as well.

[84][85][86] Human inputs of phosphate further encourage these red tides, so strong interest exists in learning more about dinoflagellates, from both medical and economic perspectives.

Dinoflagellates are known to be particularly capable of scavenging dissolved organic phosphorus for P-nutrient, several HAS species have been found to be highly versatile and mechanistically diversified in utilizing different types of DOPs.

[96] Within the United States, Central Florida is home to the Indian River Lagoon which is abundant with dinoflagellates in the summer and bioluminescent ctenophore in the winter.

[101] This takes place by fusion of two individuals to form a zygote, which may remain mobile in typical dinoflagellate fashion and is then called a planozygote.

Unlike in higher plants most of this variability, for example in dormancy periods, has not been proven yet to be attributed to latitude adaptation or to depend on other life cycle traits.

[105][106] Thus, despite recent advances in the understanding of the life histories of many dinoflagellate species, including the role of cyst stages, many gaps remain in knowledge about their origin and functionality.

This attribution was coincident with evolutionary theories about the origin of eukaryotic cell fusion and sexuality, which postulated advantages for species with diploid resting stages, in their ability to withstand nutrient stress and mutational UV radiation through recombinational repair, and for those with haploid vegetative stages, as asexual division doubles the number of cells.

[110][103] However, in the general life cycle of cyst-producing dinoflagellates as outlined in the 1960s and 1970s, resting cysts were assumed to be the fate of sexuality,[100][111] which itself was regarded as a response to stress or unfavorable conditions.

Sexuality involves the fusion of haploid gametes from motile planktonic vegetative stages to produce diploid planozygotes that eventually form cysts, or hypnozygotes, whose germination is subject to both endogenous and exogenous controls.

[114][115] Further, in 2006 Kremp and Parrow showed the dormant resting cysts of the Baltic cold water dinoflagellates Scrippsiella hangoei and Gymnodinium sp.

Loss of the standard stop codons, trans-splicing of mRNAs for the mRNA of cox3, and extensive RNA editing recoding of most genes has occurred.

Dinoflagellates are mainly represented as fossils by dinocysts, which have a long geological record with lowest occurrences during the mid-Triassic,[134] whilst geochemical markers suggest a presence to the Early Cambrian.

[149] Some groups that have lost the photosynthetic properties of their original red algae plastids has obtained new photosynthetic plastids (chloroplasts) through so-called serial endosymbiosis, both secondary and tertiary: Some species also perform kleptoplasty: Dinoflagellate evolution has been summarized into five principal organizational types: prorocentroid, dinophysoid, gonyaulacoid, peridinioid, and gymnodinoid.