The Dinoflagellates (), also called Dinophytes, are a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group of single-celled

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s constituting the phylum Dinoflagellata and are usually considered

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s. Dinoflagellates are mostly marine

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

, but they are also common in freshwater habitats. Their populations vary with

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

, and depth. Many dinoflagellates are

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

, but a large fraction of these are in fact

mixotrophic A mixotroph is an organism that uses a mix of different sources of energy and carbon, instead of having a single trophic mode, on the continuum from complete autotrophy to complete heterotrophy. It is estimated that mixotrophs comprise more than ...

, combining photosynthesis with ingestion of prey (

phagotrophy Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

and

myzocytosis Myzocytosis (from Greek: myzein, (') meaning "to suck" and kytos (') meaning "container", hence referring to "cell") is a method of feeding found in some heterotrophic organisms. It is also called "cellular vampirism" as the predatory cell pierce ...

). In terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, although substantially smaller than

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s. Some species are

endosymbiont An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...

s of marine animals and play an important part in the biology of

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

s. Other dinoflagellates are unpigmented predators on other protozoa, and a few forms are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

(for example, ''

Oodinium ''Oodinium'' is a genus of parasitic dinoflagellates. Their hosts are salt- and fresh-water fish, causing a type of fish velvet disease (also called gold dust disease). One species has also been recorded on various cnidarians. The host typ ...

'' and ''

Pfiesteria ''Pfiesteria'' is a genus of heterotrophic dinoflagellates that has been associated with harmful algal blooms and fish kills. ''Pfiesteria'' complex organisms (PCOs) were claimed to be responsible for large fish kills in the 1980s and 1990s on th ...

''). Some dinoflagellates produce resting stages, called dinoflagellate cysts or

dinocyst Dinocysts or dinoflagellate cysts are typically 15 to 100 μm in diameter and produced by dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic-walled dinocysts are often ...

s, as part of their lifecycles; this occurs in 84 of the 350 described freshwater species and a little more than 10% of the known marine species. Dinoflagellates are

alveolate The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major unranked clade or superphylum within Eukaryota. They are currently grouped with the Stramenopiles and Rhizaria among the protists with tubulocristate ...

s possessing two

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

, the ancestral condition of

bikont A bikont ("two flagella") is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella. Enzymes Anothe ...

s. About 1,555 species of free-living marine dinoflagellates are currently described. Another estimate suggests about 2,000 living species, of which more than 1,700 are marine (free-living, as well as benthic) and about 220 are from fresh water. The latest estimates suggest a total of 2,294 living dinoflagellate species, which includes marine, freshwater, and parasitic dinoflagellates. A rapid accumulation of certain dinoflagellates can result in a visible coloration of the water, colloquially known as

red tide A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

harmful algal bloom A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

), which can cause

shellfish poisoning Shellfish poisoning includes four syndromes that share some common features and are primarily associated with bivalve molluscs (such as mussels, clams, oysters and scallops.) As filter feeders, these shellfish may accumulate toxins produced by m ...

if humans eat contaminated shellfish. Some dinoflagellates also exhibit

bioluminescence Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...

, primarily emitting blue-green light, which may be visible in oceanic areas under certain conditions.

Etymology

The term "dinoflagellate" is a combination of the Greek ''dinos'' and the Latin ''flagellum''. ''Dinos'' means "whirling" and signifies the distinctive way in which dinoflagellates were observed to swim. ''Flagellum'' means "whip" and this refers to their

History

In 1753, the first modern dinoflagellates (''Noctiluca'', although not formally named until 1816) were described by Henry Baker as "Animalcules which cause the Sparkling Light in Sea Water",.

Otto Friedrich Müller Otto Friedrich Müller, also known as Otto Friedrich Mueller (2 November 1730 – 26 December 1784) was a Denmark, Danish natural history, naturalist and scientific illustrator. Biography Müller was born in Copenhagen. He was educated for the ch ...

recorded ''Bursaria'' (now ''Ceratium'') ''hirundinella'' and ''Vorticella'' (now ''Peridinium'') ''cinctum'' in 1773. The oldest generic name for a Dinoflagellate is ''Ceratium'', which was proposed by Schrank (1793). In the 1830s, the German microscopist

Christian Gottfried Ehrenberg Christian Gottfried Ehrenberg (19 April 1795 – 27 June 1876) was a German Natural history, naturalist, zoologist, Botany, botanist, comparative anatomist, geologist, and microscopy, microscopist. He is considered to be one of the most famous an ...

examined many water and plankton samples and proposed several dinoflagellate genera that are still used today including ''Peridinium, Prorocentrum'', and ''Dinophysis''. These same dinoflagellates were first defined by

Otto Bütschli Johann Adam Otto Bütschli (3 May 1848 – 2 February 1920) was a German zoologist and professor at the University of Heidelberg. He specialized in invertebrates and insect development. Many of the groups of protists were first recognized by him. ...

in 1885 as the

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

order Dinoflagellida. Botanists treated them as a division of algae, named Pyrrophyta or Pyrrhophyta ("fire algae"; Greek ''pyrr(h)os'', fire) after the bioluminescent forms, or Dinophyta. At various times, the

cryptomonad The cryptomonads (or cryptophytes) are a superclass of algae, most of which have plastids. They are traditionally considered a division of algae among phycologists, under the name of Cryptophyta. They are common in freshwater, and also occur ...

s, ebriids, and ellobiopsids have been included here, but only the last are now considered close relatives. Dinoflagellates have a known ability to transform from noncyst to cyst-forming strategies, which makes recreating their evolutionary history extremely difficult.

Morphology

Dinoflagellates are unicellular and possess two dissimilar flagella arising from the ventral cell side (dinokont flagellation). They have a ribbon-like transverse flagellum with multiple waves that beats to the cell's left, and a more conventional one, the longitudinal flagellum, that beats posteriorly. 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 axonemal edge has simple hairs that can be of varying lengths. The flagellar movement produces forward propulsion and also a turning force. The longitudinal flagellum is relatively conventional in appearance, with few or no hairs. It beats with only one or two periods to its wave. 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. In dinoflagellate species with desmokont flagellation (e.g., ''

Prorocentrum The Prorocentrales are a small order of dinoflagellates. They are distinguished by having their two flagella inserted apically, rather than ventrally as in other groups. One flagellum extends forward and the other circles its base, and there are ...

''), the two flagella are differentiated as in dinokonts, but they are not associated with grooves. Dinoflagellates have a complex cell covering called an amphiesma or cortex, composed of a series of membranes, flattened

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features ...

s called alveoli (= amphiesmal vesicles) and related structures. In In thecate ("armoured") dinoflagellates, these support overlapping

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

plates to create a sort of armor called the theca or lorica, as opposed to athecate ("nude") dinoflagellates. These occur in various shapes and arrangements, depending on the species and sometimes on the stage of the dinoflagellate. Conventionally, the term tabulation has been used to refer to this arrangement of thecal plates. The plate configuration can be denoted with the plate formula or tabulation formula. Fibrous

extrusome Extrusomes are membrane-bound organelles found in eukaryotic cells that are capable of discharging material contained within to the exterior of the cell. Due to the diversity in structure and function, it is unlikely that different types of extruso ...

s are also found in many forms. A transverse groove, the so-called cingulum (or cigulum) runs around the cell, thus dividing it into an anterior (episoma) and posterior (hyposoma). If and only if a theca is present, the parts are called epitheca and hypotheca, respectively. Posteriorly, starting from the transverse groove, there is a longitudinal furrow called the sulcus. The transverse flagellum strikes in the cingulum, the longitudinal flagellum in the sulcus. Together with various other structural and genetic details, this organization indicates a close relationship between the dinoflagellates, the

Apicomplexa The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an ap ...

, and

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s, collectively referred to as the

s. Dinoflagellate tabulations can be grouped into six "tabulation types": gymnodinoid, suessoid, gonyaulacoid– peridinioid, nannoceratopsioid, dinophysioid, and prorocentroid. Most Dinoflagellates have a plastid derived from secondary endosymbiosis of red algae, however dinoflagellates with plastids derived from green algae and tertiary endosymbiosis of diatoms have also been discovered. Similar to other photosynthetic organisms, dinoflagellates contain

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

s ''a'' and c2 and the carotenoid beta-carotene. Dinoflagellates also produce the

xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", an ...

s including

peridinin Peridinin is a light-harvesting apocarotenoid, a pigment associated with chlorophyll and found in the peridinin-chlorophyll-protein (PCP) light-harvesting complex in dinoflagellates, best studied in '' Amphidinium carterae''. Biological signific ...

, dinoxanthin, and

diadinoxanthin Diadinoxanthin is a pigment found in phytoplankton. It has the formula C40H54O3. It gives rise to the xanthophylls diatoxanthin and dinoxanthin. Diadinoxanthin is a plastid pigment. Plastid pigments include chlorophylls a and c, fucoxanthin, he ...

. These

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

s give many dinoflagellates their typical golden brown color. However, the dinoflagellates ''

Karenia brevis ''Karenia brevis'' is a microscopic, single-celled, photosynthetic organism in the genus '' Karenia''. It is a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the "Florida red tides" that ...

, Karenia mikimotoi,'' and ''

Karlodinium micrum ''Karlodinium'' is a genus of athecate dinoflagellates that lives worldwide. They are often toxin producing, and compared to the other members of the Kareniaceae, are fairly small at <8-15 μm diameter. They are also able to form intense

'' have acquired other pigments through endosymbiosis, including

fucoxanthin Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. Fucoxanthin absorbs light primarily in the blue-gree ...

. This suggests their chloroplasts were incorporated by several

endosymbiotic event An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), which live in the root ...

s involving already colored or secondarily colorless forms. The discovery of

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

s in the

has led some to suggest they were inherited from an ancestor common to the two groups, but none of the more basal lines has them. All the same, the dinoflagellate cell consists of the more common organelles such as rough and smooth

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

and

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...

grains, and food

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s. Some have even been found with a light-sensitive organelle, the eyespot or stigma, or a larger nucleus containing a prominent

nucleolus The nucleolus (; : nucleoli ) is the largest structure in the cell nucleus, nucleus of eukaryote, eukaryotic cell (biology), cells. It is best known as the site of ribosome biogenesis. The nucleolus also participates in the formation of signa ...

. The dinoflagellate ''

Erythropsidinium ''Erythropsidinium'' (formerly ''Erythropsis'') is a genus of dinoflagellates (a type of unicellular eukaryote) of the family Warnowiaceae. Characteristics ''Erythropsidinium'' cells are a relatively large by dinoflagellate standards (50-120μm ...

'' has the smallest known eye. Some athecate species have an internal skeleton consisting of two star-like

siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant ...

elements that has an unknown function, and can be found as

microfossils A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

. Tappan gave a survey of dinoflagellates with internal skeletons. This included the first detailed description of the pentasters in '' Actiniscus pentasterias'', based on scanning

electron microscopy An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...

. They are placed within the order

Gymnodiniales The Gymnodiniales are an order (biology), order of dinoflagellates, of the class (biology), class Dinophyceae. Members of the order are known as gymnodinioid or gymnodinoid (terms that can also refer to any organism of similar morphology). They a ...

, suborder Actiniscineae.

Theca structure and formation

The formation of thecal plates has been studied in detail through ultrastructural studies.

The dinoflagellate nucleus: dinokaryon

'Core dinoflagellates' ( dinokaryotes) have a peculiar form of

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

, called a

dinokaryon A dinokaryon is a eukaryotic nucleus present in dinoflagellates in which the chromosomes are fibrillar in appearance (i.e. with unmasked DNA fibrils) and are more or less continuously condensed. The nuclear envelope does not break down durin ...

, in which the

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

s are attached to the

nuclear membrane The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer polar membrane, membranes that in eukaryotic cells surround the Cell nucleus, nucleus, which encloses the genome, genetic material. The nuclear envelope con ...

. These carry reduced number of

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaeal phyla. They act as spools around which DNA winds to create structural units called nucleosomes ...

s. 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. Dinoflagellate nuclei remain condensed throughout interphase rather than just during

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

, which is closed and involves a uniquely extranuclear

mitotic spindle In cell biology, the spindle apparatus is the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a process ...

. In This sort of nucleus was once considered to be an intermediate between the nucleoid region of

prokaryote A prokaryote (; less commonly spelled procaryote) is a unicellular organism, single-celled organism whose cell (biology), cell lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Gree ...

s and the true nuclei of

s, so were termed " mesokaryotic," but now are considered derived rather than primitive traits (i. e. ancestors of dinoflagellates had typical eukaryotic nuclei). In addition to dinokaryotes, DVNPs can be found in a group of basal dinoflagellates (known as Marine

Alveolate The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major unranked clade or superphylum within Eukaryota. They are currently grouped with the Stramenopiles and Rhizaria among the protists with tubulocristate ...

s, "MALVs") that branch as sister to dinokaryotes (

Syndiniales The Syndiniales are an order of early branching dinoflagellates (also known as Marine Alveolates, "MALVs"), found as parasites of crustaceans, fish, algae, cnidarians, and protists (ciliates, radiolarians, other dinoflagellates). The trophic f ...

Classification

Generality

Dinoflagellates are protists and have been classified using both the

International Code of Botanical Nomenclature The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...

(ICBN, now renamed as ICN) and the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the I ...

(ICZN). About half of living dinoflagellate species are autotrophs possessing chloroplasts and half are nonphotosynthesising heterotrophs. The

dinoflagellates, named after their peridinin plastids, appear to be ancestral for the dinoflagellate lineage. Almost half of all known species have chloroplasts, which are either the original peridinin plastids or new plastids acquired from other lineages of unicellular algae through endosymbiosis. The remaining species have lost their photosynthetic abilities and have adapted to a heterotrophic, parasitic or

kleptoplastic Kleptoplasty or kleptoplastidy is a process in symbiotic relationships whereby plastids, notably chloroplasts from algae, are sequestered by the host. The word is derived from ''Kleptes'' (κλέπτης) which is Greek for thief. The alga is eat ...

lifestyle. Most (but not all) dinoflagellates have a

, described below (see: Life cycle, below). Dinoflagellates with a dinokaryon are classified under Dinokaryota, while dinoflagellates without a dinokaryon are classified under

. Although classified as

eukaryotes The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of ...

, the dinoflagellate nuclei are not characteristically eukaryotic, as some of them lack

histones In biology, histones are highly Base (chemistry), basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaea, Archaeal Phylum, phyla. They act as spools around which DNA winds to create st ...

and nucleosomes, and maintain continually condensed chromosomes during

. The dinoflagellate nucleus was termed 'mesokaryotic' by Dodge (1966), due to its possession of intermediate characteristics between the coiled DNA areas of prokaryotic bacteria and the well-defined eukaryotic nucleus. This group, however, does contain typically eukaryotic

organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

, such as Golgi bodies, mitochondria, and chloroplasts. Jakob Schiller (1931–1937) provided a description of all the species, both marine and freshwater, known at that time. Later, Alain Sournia (1973, 1978, 1982, 1990, 1993) listed the new taxonomic entries published after Schiller (1931–1937). Sournia (1986) gave descriptions and illustrations of the marine genera of dinoflagellates, excluding information at the species level. The latest index is written by Gómez.

Identification

English-language taxonomic monographs covering large numbers of species are published for the Gulf of Mexico, the Indian Ocean, the British Isles, the Mediterranean and the North Sea. The main source for identification of freshwater dinoflagellates is the ''Süsswasser Flora''.

Calcofluor-white Calcofluor-white or CFW is a fluorescent blue dye used in biology and textiles. It binds to 1–3 beta and 1–4 beta polysaccharides of chitin and cellulose that are present in cell walls on fungi, plants, and algae. In plant cell biology re ...

can be used to stain thecal plates in armoured dinoflagellates.

Ecology and physiology

Habitats

Dinoflagellates are found in all aquatic environments: marine, brackish, and fresh water, including in snow or ice. They are also common in benthic environments and sea ice.

Endosymbionts

All

Zooxanthellae Zooxanthellae (; zooxanthella) is a colloquial term for single-celled photosynthetic organisms that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, demosponges, and nudibranchs. Most known zooxanthell ...

are dinoflagellates and most of them are members within Symbiodiniaceae (e.g., the genus ''

Symbiodinium ''Symbiodinium'' is a genus of dinoflagellates that encompasses the largest and most prevalent group of endosymbiotic dinoflagellates known and have photosymbiotic relationships with many species. These unicellular microalgae commonly reside in ...

''). The association between ''Symbiodinium'' and reef-building

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s is widely known. However, endosymbiontic

inhabit a great number of other invertebrates and protists, for example many sea anemones,

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

nudibranchs Nudibranchs () are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have be ...

, the giant clam ''

Tridacna ''Tridacna'' is a genus of large saltwater clams, Marine (ocean), marine bivalve molluscs in the subfamily Tridacninae, the giant clams. Many Tridacna species are threatened. They have heavy shells, fluted with 4 to 6 folds. The Mantle (mollus ...

'', and several species of

radiolarians The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ecto ...

and

foraminiferans Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

. Many extant dinoflagellates are

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

(here defined as organisms that eat their prey from the inside, i.e.

endoparasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

, or that remain attached to their prey for longer periods of time, i.e. ectoparasites). They can parasitize animal or protist hosts. ''Protoodinium, Crepidoodinium, Piscinoodinium'', and ''Blastodinium'' retain their plastids while feeding on their zooplanktonic or fish hosts. In most parasitic dinoflagellates, the infective stage resembles a typical motile dinoflagellate cell.

Nutritional strategies

Three nutritional strategies are seen in dinoflagellates:

phototroph Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a list of common m ...

mixotroph A mixotroph is an organism that uses a mix of different sources of energy and carbon, instead of having a single trophic mode, on the continuum from complete autotrophy to complete heterotrophy. It is estimated that mixotrophs comprise more than ...

y, and

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

y. Phototrophs can be

photoautotroph Photoautotrophs are organisms that can utilize light energy from sunlight, and elements (such as carbon) from inorganic compounds, to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). Such biological activitie ...

s or auxotrophs. Mixotrophic dinoflagellates are photosynthetically active, but are also heterotrophic. Facultative mixotrophs, in which autotrophy or heterotrophy is sufficient for nutrition, are classified as amphitrophic. If both forms are required, the organisms are mixotrophic ''sensu stricto''. Some free-living dinoflagellates do not have chloroplasts, but host a phototrophic endosymbiont. A few dinoflagellates may use alien chloroplasts (cleptochloroplasts), obtained from food (

kleptoplasty Kleptoplasty or kleptoplastidy is a process in symbiosis, symbiotic relationships whereby plastids, notably chloroplasts from algae, are sequestered by the host. The word is derived from ''Kleptes'' (κλέπτης) which is Greek language, Greek ...

). Some dinoflagellates may feed on other organisms as predators or parasites. Food inclusions contain bacteria, bluegreen algae, diatoms, ciliates, and other dinoflagellates. Mechanisms of capture and ingestion in dinoflagellates are quite diverse. Several dinoflagellates, both thecate (e.g. ''Ceratium hirundinella'', ''Peridinium globulus'') and nonthecate (e.g. ''Oxyrrhis marina'', ''Gymnodinium'' sp. and ''Kofoidinium'' spp.), draw prey to the sulcal region of the cell (either via water currents set up by the flagella or via pseudopodial extensions) and ingest the prey through the sulcus. 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). ''Oblea'', ''Zygabikodinium'', and ''Diplopsalis'' are the only other dinoflagellate genera known to use this particular feeding mechanism. ''Gymnodinium fungiforme'', commonly found as a contaminant in algal or ciliate cultures, feeds by attaching to its prey and ingesting prey cytoplasm through an extensible peduncle. Two related genera, ''Polykrikos'' and ''Neatodinium'', shoot out a harpoon-like organelle to capture prey. Some mixotrophic dinoflagellates are able to produce neurotoxins that have anti-grazing effects on larger copepods and enhance the ability of the dinoflagellate to prey upon larger copepods. Toxic strains of ''Karlodinium veneficum'' produce karlotoxin that kills predators who ingest them, thus reducing predatory populations and allowing blooms of both toxic and non-toxic strains of ''K. veneficum''. Further, the production of karlotoxin enhances the predatory ability of ''K. veneficum'' by immobilizing its larger prey. ''K. armiger'' are more inclined to prey upon copepods by releasing a potent neurotoxin that immobilizes its prey upon contact. When ''K. armiger'' are present in large enough quantities, they are able to cull whole populations of their copepod prey. The feeding mechanisms of the oceanic dinoflagellates remain unknown, although pseudopodial extensions were observed in ''Podolampas bipes''.

Pigments in dinoflagellates

Dinoflagellates possess a distinctive suite of photosynthetic pigments that allow them to survive and grow in a variety of aquatic environments. Like other phytoplankton, many dinoflagellates contain chlorophyll a and chlorophyll c, which are essential for photosynthesis and light energy capture. However, unlike green algae and higher plants, they lack chlorophyll b. Instead, they utilize chlorophyll c2, which is more efficient for absorbing blue-green light, making them well adapted to low-light or deeper water conditions. These pigments, along with carotenoids, contribute to the characteristic coloration of dinoflagellates, which can range from golden-brown to red. A unique pigment in dinoflagellates is peridinin, a specialized carotenoid that plays a key role in light harvesting and energy transfer to chlorophyll a. 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. 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. These pigments are necessary for photoacclimation, allowing dinoflagellates to survive under fluctuating light conditions. Not all dinoflagellates rely solely on photosynthetic pigments for energy. Many species are heterotrophic or mixotrophic, meaning they can acquire nutrients through both photosynthesis and predation. Symbiotic dinoflagellates, such as Symbiodinium, play a important ecological role by forming mutualistic relationships with corals, where their pigments drive photosynthesis and energy production that sustain coral reef ecosystems. The unique pigment composition of dinoflagellates also contributes to large-scale phenomena such as harmful algal blooms and red tides, where high concentrations of pigmented cells cause dramatic discoloration of coastal waters and can produce toxic effects.

Blooms

Introduction

Dinoflagellate blooms are generally unpredictable, short, with low species diversity, and with little species succession. The low species diversity can be due to multiple factors. One way a lack of diversity may occur in a bloom is through a reduction in predation and a decreased competition. The first may be achieved by having predators reject the dinoflagellate, by, for example, decreasing the amount of food it can eat. This additionally helps prevent a future increase in predation pressure by causing predators that reject it to lack the energy to breed. A species can then inhibit the growth of its competitors, thus achieving dominance.

Harmful algal blooms

Dinoflagellates sometimes bloom in concentrations of more than a million cells per millilitre. Under such circumstances, they can produce toxins (generally called

dinotoxin Dinotoxins are a group of toxins which are produced by flagellate, aquatic, unicellular protists called dinoflagellates. Dinotoxin was coined by Hardy and Wallace in 2012 as a general term for the variety of toxins produced by dinoflagellates. Dinof ...

s) in quantities capable of killing fish and accumulating in filter feeders such as

shellfish Shellfish, in colloquial and fisheries usage, are exoskeleton-bearing Aquatic animal, aquatic invertebrates used as Human food, food, including various species of Mollusca, molluscs, crustaceans, and echinoderms. Although most kinds of shellfish ...

, which in turn may be passed on to people who eat them. This phenomenon is called a

, from the color the bloom imparts to the water. Some colorless dinoflagellates may also form toxic blooms, such as ''

''. Some dinoflagellate blooms are not dangerous. Bluish flickers visible in ocean water at night often come from blooms of

bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...

dinoflagellates, which emit short flashes of light when disturbed. A red tide occurs because dinoflagellates are able to reproduce rapidly and copiously as a result of the abundant nutrients in the water. They contain

toxin A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...

s that affect surrounding marine life and people who consume them. A specific carrier is

, which can introduce both nonfatal and fatal illnesses. One such poison is

saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin. Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralytic she ...

, a powerful

paralytic Paralysis (: paralyses; also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, ...

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

. Human inputs of

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

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. The ecology of

s is extensively studied.

Bioluminescence

At night, water can have an appearance of sparkling light due to the bioluminescence of dinoflagellates. More than 18 genera of dinoflagellates are bioluminescent, and the majority of them emit a blue-green light. These species contain scintillons, individual cytoplasmic bodies (about 0.5 μm in diameter) distributed mainly in the cortical region of the cell, outpockets of the main cell vacuole. They contain dinoflagellate luciferase, the main enzyme involved in dinoflagellate bioluminescence, and

luciferin Luciferin () is a generic term for the light-emitting chemical compound, compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with Oxygen, molecular oxygen. The resulting transforma ...

, a chlorophyll-derived tetrapyrrole ring that acts as the substrate to the light-producing reaction. The luminescence occurs as a brief (0.1 sec) blue flash (max 476 nm) when stimulated, usually by mechanical disturbance. Therefore, when mechanically stimulated—by boat, swimming, or waves, for example—a blue sparkling light can be seen emanating from the sea surface. Dinoflagellate bioluminescence is controlled by a circadian clock and only occurs at night. Luminescent and nonluminescent strains can occur in the same species. The number of scintillons is higher during night than during day, and breaks down during the end of the night, at the time of maximal bioluminescence. The luciferin-luciferase reaction responsible for the bioluminescence is pH sensitive. When the pH drops, luciferase changes its shape, allowing luciferin, more specifically tetrapyrrole, to bind. Dinoflagellates can use bioluminescence as a defense mechanism. They can startle their predators by their flashing light or they can ward off potential predators by an indirect effect such as the "burglar alarm". The bioluminescence attracts attention to the dinoflagellate and its attacker, making the predator more vulnerable to predation from higher trophic levels. Bioluminescent dinoflagellate ecosystem bays are among the rarest and most fragile, with the most famous ones being the Bioluminescent Bay in La Parguera, Lajas, Puerto Rico; Mosquito Bay in

Vieques, Puerto Rico Vieques (; ), officially Isla de Vieques, is an island, Culebra barrio-pueblo, town and Municipalities of Puerto Rico, municipality of Puerto Rico, and together with Culebra, Puerto Rico, Culebra, it is geographically part of the Spanish Virgin ...

; and Las Cabezas de San Juan Reserva Natural

Fajardo, Puerto Rico Fajardo () is a town and a municipality part of the San Juan-Caguas-Fajardo Combined Statistical Area in Puerto Rico. Fajardo is the hub of much of the recreational boating in Puerto Rico and a popular launching port to Culebra, Vieques, and ...

. Also, a bioluminescent lagoon is near Montego Bay, Jamaica, and bioluminescent harbors surround Castine, Maine. Within the United States, Central Florida is home to the

Indian River Lagoon The Indian River Lagoon is a grouping of three lagoons: the Mosquito Lagoon, the Banana River, and the Indian River, on the Atlantic Coast of Florida; one of the most biodiverse estuaries in the Northern Hemisphere and is home to more than 4, ...

which is abundant with dinoflagellates in the summer and bioluminescent ctenophore in the winter.

Lipid and sterol production

Dinoflagellates produce characteristic lipids and sterols. One of these sterols is typical of dinoflagellates and is called dinosterol.

Transport

Dinoflagellate

theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...

can sink rapidly to the seafloor in

marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...

Life cycle

Introduction

Dinoflagellates have a

haplontic life cycle In biology, a biological life cycle (or just life cycle when the biological context is clear) is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offsp ...

, with the possible exception of ''

Noctiluca ''Noctiluca scintillans'' is a marine species of dinoflagellate that can exist in a green or red form, depending on the pigmentation in its vacuoles. It can be found worldwide, but its geographical distribution varies depending on whether it ...

'' and its relatives. The life cycle usually involves asexual reproduction by means of mitosis, either through desmoschisis or eleuteroschisis. More complex life cycles occur, more particularly with parasitic dinoflagellates. Sexual reproduction also occurs, though this mode of reproduction is only known in a small percentage of dinoflagellates. This takes place by fusion of two individuals to form a

zygote A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individ ...

, which may remain mobile in typical dinoflagellate fashion and is then called a planozygote. This zygote may later form a resting stage or hypnozygote, which is called a dinoflagellate cyst or

. After (or before) germination of the cyst, the hatchling undergoes

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

to produce new

haploid cell Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

s. Dinoflagellates appear to be capable of carrying out several

DNA repair DNA repair is a collection of processes by which a cell (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...

processes that can deal with different types of

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is constantly modified ...

Dinoflagellate cysts

The life cycle of many dinoflagellates includes at least one nonflagellated benthic stage as a

cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubb ...

. Different types of dinoflagellate cysts are mainly defined based on morphological (number and type of layers in the cell wall) and functional (long- or short-term endurance) differences. These characteristics were initially thought to clearly distinguish pellicle (thin-walled) cysts from resting (double-walled) dinoflagellate cysts. The former were considered short-term (temporal) and the latter long-term (resting) cysts. However, during the last two decades further knowledge has highlighted the great intricacy of dinoflagellate life histories. Resting cysts of dinoflagellates

More than 10% of the approximately 2000 known marine dinoflagellate species produce cysts as part of their life cycle (see diagram on the right). These benthic phases play an important role in the ecology of the species, as part of a planktonic-benthic link in which the cysts remain in the sediment layer during conditions unfavorable for vegetative growth and, from there, reinoculate the water column when favorable conditions are restored. Indeed, during dinoflagellate evolution the need to adapt to fluctuating environments and/or to seasonality is thought to have driven the development of this life cycle stage. Most protists form dormant cysts in order to withstand starvation and UV damage. However, there are enormous differences in the main phenotypic, physiological and resistance properties of each dinoflagellate species cysts. Unlike in higher plants most of this variability, for example in

dormancy Dormancy is a period in an organism's Biological life cycle, life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolism, metabolic activity and therefore helps an organism to conserv ...

periods, has not been proven yet to be attributed to latitude adaptation or to depend on other life cycle traits. 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. Recognition of the capacity of dinoflagellates to encyst dates back to the early 20th century, in

biostratigraphic Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

studies of fossil dinoflagellate cysts. Paul Reinsch was the first to identify cysts as the fossilized remains of dinoflagellates. Later, cyst formation from gamete fusion was reported, which led to the conclusion that encystment is associated with sexual reproduction. These observations also gave credence to the idea that microalgal encystment is essentially a process whereby zygotes prepare themselves for a dormant period. Because the resting cysts studied until that time came from sexual processes, dormancy was associated with sexuality, a presumption that was maintained for many years. 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. Nonetheless, certain environmental conditions may limit the advantages of recombination and sexuality, such that in fungi, for example, complex combinations of haploid and diploid cycles have evolved that include asexual and sexual resting stages. 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, 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 Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell. For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...

and

exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It is the opposite of endogeneity or endogeny, the fact of being influenced from within a system. Economics In an economic model, an ...

controls. Endogenously, a species-specific physiological maturation minimum period (dormancy) is mandatory before germination can occur. Thus, hypnozygotes were also referred to as "resting" or "resistant" cysts, in reference to this physiological trait and their capacity following dormancy to remain viable in the sediments for long periods of time. Exogenously, germination is only possible within a window of favorable environmental conditions. Yet, with the discovery that planozygotes were also able to divide it became apparent that the complexity of dinoflagellate life cycles was greater than originally thought. Following corroboration of this behavior in several species, the capacity of dinoflagellate sexual phases to restore the vegetative phase, bypassing cyst formation, became well accepted. Further, in 2006 Kremp and Parrow showed the dormant resting cysts of the Baltic cold water dinoflagellates '' Scrippsiella hangoei'' and ''

Gymnodinium ''Gymnodinium'' is a genus of dinoflagellates, a type of marine and freshwater plankton. It is one of the few naked dinoflagellates, or species lacking armor known as cellulosic plates. Since 2000, the species which had been considered to be part ...

'' sp. were formed by the direct encystment of haploid vegetative cells, i.e., asexually. In addition, for the zygotic cysts of ''

Pfiesteria piscicida ''Pfiesteria piscicida'' is a dinoflagellate species of the genus ''Pfiesteria'' that some researchers claim was responsible for many harmful algal blooms in the 1980s and 1990s on the coast of North Carolina and Maryland. North Carolinian media ...

'' dormancy was not essential.

Genomics

One of the most striking features of dinoflagellates is the large amount of cellular DNA that they contain. Most eukaryotic algae contain on average about 0.54 pg DNA/cell, whereas estimates of dinoflagellate DNA content range from 3–250 pg/cell, corresponding to roughly 3000–215 000 Mb (in comparison, the haploid human genome is 3180 Mb and hexaploid ''Triticum'' wheat is 16 000 Mb).

Polyploidy Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

or polyteny may account for this large cellular DNA content, but earlier studies of DNA reassociation kinetics and recent genome analyses do not support this hypothesis. Rather, this has been attributed, hypothetically, to the rampant retroposition found in dinoflagellate genomes. In addition to their disproportionately large genomes, dinoflagellate nuclei are unique in their morphology, regulation, and composition. Their DNA is so tightly packed that exactly how many chromosomes they have is still uncertain. The dinoflagellates share an unusual mitochondrial genome organisation with their relatives, the

. Both groups have very reduced mitochondrial genomes (around 6 kilobases (kb) in the Apicomplexa vs ~16kb for human mitochondria). One species, '' Amoebophrya ceratii'', has lost its mitochondrial genome completely, yet still has functional mitochondria. The genes on the dinoflagellate genomes have undergone a number of reorganisations, including massive genome amplification and recombination which have resulted in multiple copies of each gene and gene fragments linked in numerous combinations. 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. The reasons for this transformation are unknown. In a small group of dinoflagellates, called 'dinotoms' (Durinskia and Kryptoperidinium), the endosymbionts (diatoms) still have mitochondria, making them the only organisms with two evolutionarily distinct mitochondria. In most of the species, the plastid genome consist of just 14 genes. The DNA of the plastid in the peridinin-containing dinoflagellates is contained in a series of small circles called minicircles. Each circle contains one or two polypeptide genes. The genes for these polypeptides are chloroplast-specific because their homologs from other photosynthetic eukaryotes are exclusively encoded in the chloroplast genome. Within each circle is a distinguishable 'core' region. Genes are always in the same orientation with respect to this core region. In terms of

DNA barcoding DNA barcoding is a method of species identification using a short section of DNA from a specific gene or genes. The premise of DNA barcoding is that by comparison with a reference library of such DNA sections (also called " sequences"), an indiv ...

, ITS sequences can be used to identify species, where a genetic distance of p≥0.04 can be used to delimit species, which has been successfully applied to resolve long-standing taxonomic confusion as in the case of resolving the Alexandrium tamarense complex into five species. A recent study revealed a substantial proportion of dinoflagellate genes encode for unknown functions, and that these genes could be conserved and lineage-specific.

Evolutionary history

Dinoflagellates are mainly represented as fossils by

dinocysts Dinocysts or dinoflagellate cysts are typically 15 to 100 μm in diameter and produced by dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic-walled dinocysts are ofte ...

, which have a long geological record with lowest occurrences during the mid-

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

, whilst geochemical markers suggest a presence to the Early Cambrian. Some evidence indicates dinosteroids in many

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

and

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

rocks might be the product of ancestral dinoflagellates (protodinoflagellates). Dinoflagellates show a classic radiation of morphologies during the Late Triassic through the Middle Jurassic. More modern-looking forms proliferate during the later Jurassic and Cretaceous. This trend continues into the Cenozoic, albeit with some loss of diversity. Molecular phylogenetics show that dinoflagellates are grouped with

ciliates The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...

and apicomplexans (=Sporozoa) in a well-supported clade, the

alveolates The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major unranked clade or superphylum within Eukaryota. They are currently grouped with the Stramenopiles and Rhizaria among the protists with tubulocristat ...

. The closest relatives to dinokaryotic dinoflagellates appear to be apicomplexans, ''Perkinsus, Parvilucifera'', syndinians, and ''Oxyrrhis''. Molecular phylogenies are similar to phylogenies based on morphology. The earliest stages of dinoflagellate evolution appear to be dominated by parasitic lineages, such as perkinsids and syndinians (e.g. ''Amoebophrya'' and ''Hematodinium''). All dinoflagellates contain red algal plastids or remnant (nonphotosynthetic) organelles of red algal origin. The parasitic dinoflagellate ''Hematodinium'' however lacks a plastid entirely. 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: * '' Lepidodinium'' unusually possesses a green algae-derived plastid (all other serially-acquired plastids can be traced back to red algae). The plastid is most related to free-living '' Pedinomonas'' (hence likely secondary). Two previously undescribed dinoflagellates ("MGD" and "TGD") contain a closely-related plastid. * ''Karenia'', ''Karlodinium'', and ''Takayama'' possess plastids of

haptophyte The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...

origin, produced in three separate events. * "Dinotoms" (''Durinskia'' and ''Kryptoperidinium'') have plastids derived from

s. Some species also perform

: * ''

Dinophysis ''Dinophysis'' is a genus of dinoflagellatesAlgaeBase''Dinophysis'' Ehrenberg, 1839/ref> common in tropical, temperate, coastal and oceanic waters.Hallegraeff, G.M., Lucas, I.A.N. 1988: The marine dinoflagellate genus Dinophysis (Dinophyceae): ph ...

'' have plastids from a

, due to kleptoplasty from a cilate prey.Kim, M., Nam, S. W., Shin, W., Coats, D. W. and Park, M. G. 2012: ''Dinophysis caudata'' (Dinophyceae) sequesters and retains plastids from the mixotrophic ciliate prey ''Mesodinium Rubrum''. Journal of Phycology, 48: 569-579. doi:10.1111/j.1529-8817.2012.01150.x * The Kareniaceae (which contains the three haptophyte-having genera) contains two separate cases of kleptoplasty. Dinoflagellate evolution has been summarized into five principal organizational types: prorocentroid, dinophysoid, gonyaulacoid, peridinioid, and gymnodinoid. The transitions of marine species into fresh water have been frequent events during the diversification of dinoflagellates and have occurred recently. Many dinoflagellates also have a symbiotic relationship with cyanobacteria, called cyanobionts, which have a reduced genome and has not been found outside their hosts. The Dinophysoid dinoflagellates have two genera, Amphisolenia and Triposolenia, that contain intracellular cyanobionts, and four genera; Citharistes, Histioneis, Parahistioneis, and Ornithocercus, that contain extracellular cyanobionts. Most of the cyanobionts are used for nitrogen fixation, not for photosynthesis, but some don't have the ability to fix nitrogen. The dinoflagellate ''Ornithocercus magnificus'' is host for symbionts which resides in an extracellular chamber. While it is not fully known how the dinoflagellate benefit from it, it has been suggested it is farming the cyanobacteria in specialized chambers and regularly digest some of them. Recently, the

living fossil A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of or ...

'' Dapsilidinium pastielsii'' was found inhabiting the Indo-Pacific Warm Pool, which served as a refugium for thermophilic dinoflagellates, and others such as '' Calciodinellum operosum'' and '' Posoniella tricarinelloides'' were also described from fossils before later being found alive.

Examples

* '' Alexandrium'' * ''

Gonyaulax ''Gonyaulax'' is a genus of dinoflagellates with the type species ''Gonyaulax spinifera'' (Claparède et Lachmann) Diesing. ''Gonyaulax'' belongs to red dinoflagellates and commonly causes red tides. It can produce yesotoxins: for example, strai ...

'' * ''

'' * '' Lingulodinium polyedrum'' Image:Oxyrrhis marina.jpg, '' Oxyrrhis marina'' (

Oxyrrhea ''Oxyrrhis'' is a genus of heterotrophic dinoflagellate, the only genus in the family Oxyrrhinaceae. It inhabits a range of marine environments worldwide and is important in the food web dynamics of these ecosystems. It has the potential to be co ...

) Dinophysis acuminata.jpg, '' Dinophysis acuminata'' (

Dinophyceae Dinophyceae is a class of dinoflagellates. Taxonomy * Class Dinophyceae Pascher 1914 eridinea Ehrenberg 1830 stat. nov. Wettstein; Blastodiniphyceae Fensome et al. 1993 orthog. emend.** Order Haplozoonales aplozooidea Poche 1913*** Famil ...

) Image:Ceratium sp umitunoobimusi.jpg, '' Ceratium macroceros'' (Dinophyceae) Image:Ceratium furca.jpg, ''Ceratium furcoides'' (Dinophyceae) File:Dinoflagellate - SEM MUSE.tif, Unknown dinoflagellate under SEM (Dinophyceae) Image:Pfiesteria shumwayae.jpg, '' Pfiesteria shumwayae'' (Dinophyceae) File:Symbiodinium.png, ''

'' sp. (Dinophyceae): zooxanthella, a coral endosymbiont Image:Noctiluca scintillans varias.jpg, '' Noctiluca scintillans'' (

Noctiluciphyceae The Noctilucales are an order of marine dinoflagellates. They differ from most others in that the mature cell is diploid and its nucleus does not show a dinokaryotic organization. They show gametic meiosis. Characteristics These cells are very ...

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References

Bibliography

* *

External links

International Society for the Study of Harmful AlgaeClassic dinoflagellate monographs

ttps://web.archive.org/web/20080930064242/http://www.tafi.org.au/ Tasmanian Aquaculture & Fisheries Institutebr>Tree of Life Dinoflagellates

Centre of Excellence for Dinophyte Taxonomy CEDiTDinoflagellates
* * {{Authority control Endosymbiotic events Olenekian first appearances Extant Early Triassic first appearances

Etymology

History

Morphology

Theca structure and formation

The dinoflagellate nucleus: dinokaryon

Classification

Generality

Identification

Ecology and physiology

Habitats

Endosymbionts

Nutritional strategies

Pigments in dinoflagellates

Blooms

Introduction

Harmful algal blooms

Bioluminescence

Lipid and sterol production

Transport

Life cycle

Introduction

Dinoflagellate cysts

Genomics

Evolutionary history

Examples

See also

References

Bibliography

External links