dinoflagellate dinoflagellate the dinoflagellates (greek δῖνος dinos "whirling" and latin flagellum "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum dinoflagellata and are usually considered algae. dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. their populations vary with sea surface temperature, salinity, and depth. many dinoflagellates are photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy and myzocytosis). dinoflagellatetemporal range: triassic or earlier–present ceratium sp. scientific classification domain: eukaryota clade: diaphoretickes clade: sar clade: alveolata phylum: myzozoa subphylum: dinozoa superclass: dinoflagellatabütschli 1885 sensu gomez 2012 classes ellobiophyceae psammosea oxyrrhea pronoctilucea duboscquellea syndiniophyceae noctiluciphyceae dinophyceae synonyms cilioflagellata claparède & lachmann, 1868 dinophyta dillon, 1963 dinophyceae sensu pascher, 1914 pyrrophyta pascher 1914 pyrrhophycophyta papenfuss 1946 arthrodelen flagellaten stein 1883 dinomastigota margulis & sagan, 1985 dinophyta dillon, 1963 in terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, although substantially smaller than diatoms. some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. other dinoflagellates are unpigmented predators on other protozoa, and a few forms are parasitic (for example, oodinium and pfiesteria). some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their lifecycles, and are known from 84 of the 350 described freshwater species, and form a little more than 10% of the known marine species. dinoflagellates are alveolates possessing two flagella, the ancestral condition of bikonts. 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), which can cause shellfish poisoning if humans eat contaminated shellfish. some dinoflagellates also exhibit bioluminescence—primarily emitting blue-green light. thus, some parts of the ocean light up at night giving blue-green light. 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 flagella. history in 1753, the first modern dinoflagellates were described by henry baker as "animalcules which cause the sparkling light in sea water", and named by otto friedrich müller in 1773. the term derives from the greek word δῖνος (dînos), meaning whirling, and latin flagellum, a diminutive term for a whip or scourge. 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. these same dinoflagellates were first defined by otto bütschli in 1885 as the flagellate 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 cryptomonads, 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 longitudinal (l.f.) and transverse flagellum (t.f.); sack pusule (s.p.); nucleus (n). dinoflagellate anatomy 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 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 vesicles called alveoli (= amphiesmal vesicles) and related structures. in thecate ("armoured") dinoflagellates, these support overlapping cellulose 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 extrusomes 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, and ciliates, collectively referred to as the alveolates. dinoflagellate tabulations can be grouped into six "tabulation types": gymnodinoid, suessoid, gonyaulacoid–peridinioid, nannoceratopsioid, dinophysioid, and prorocentroid. the chloroplasts in most photosynthetic dinoflagellates are bound by three membranes, suggesting they were probably derived from some ingested algae. most photosynthetic species contain chlorophylls a and c2, the carotenoid beta-carotene, and a group of xanthophylls that appears to be unique to dinoflagellates, typically peridinin, dinoxanthin, and diadinoxanthin. these pigments give many dinoflagellates their typical golden brown color. however, the dinoflagellates karenia brevis, karenia mikimotoi, and karlodinium micrum have acquired other pigments through endosymbiosis, including fucoxanthin. this suggests their chloroplasts were incorporated by several endosymbiotic events involving already colored or secondarily colorless forms. the discovery of plastids in the apicomplexa 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, golgi apparatus, mitochondria, lipid and starch grains, and food vacuoles. some have even been found with a light-sensitive organelle, the eyespot or stigma, or a larger nucleus containing a prominent nucleolus. the dinoflagellate erythropsidinium has the smallest known eye. some athecate species have an internal skeleton consisting of two star-like siliceous elements that has an unknown function, and can be found as microfossils. 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. they are placed within the order gymnodiniales, suborder actiniscineae. theca structure and formation the formation of thecal plates has been studied in detail through ultrastructural studies. the dinoflagellate nucleus: dinokaryon main article: dinokaryon 'core dinoflagellates' (dinokaryotes) have a peculiar form of nucleus, called a dinokaryon, in which the chromosomes are attached to the nuclear membrane. these carry reduced number of histones. 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, which is closed and involves a uniquely extranuclear mitotic spindle. this sort of nucleus was once considered to be an intermediate between the nucleoid region of prokaryotes and the true nuclei of eukaryotes, 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 alveolates, "malvs") that branch as sister to dinokaryotes (syndiniales). classification further information: wikispecies:dinoflagellata generality 1. ornithocercus; 2. diagram; 3. exuviaella; 4. prorocentrum; 5, 6. ceratium; 7. warnowia; 8. citharistes; 9. polykrikos dinoflagellates are protists and have been classified using both the international code of botanical nomenclature (icbn, now renamed as icn) and the international code of zoological nomenclature (iczn). about half of living dinoflagellate species are autotrophs possessing chloroplasts and half are nonphotosynthesising heterotrophs. the peridinin 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 lifestyle. most (but not all) dinoflagellates have a dinokaryon, described below (see: life cycle, below). dinoflagellates with a dinokaryon are classified under dinokaryota, while dinoflagellates without a dinokaryon are classified under syndiniales. although classified as eukaryotes, the dinoflagellate nuclei are not characteristically eukaryotic, as some of them lack histones and nucleosomes, and maintain continually condensed chromosomes during mitosis. 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, such as golgi bodies, mitochondria, and chloroplasts. dinophytic microalga isolated from sediments of amur bay 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 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 are dinoflagellates and most of them are members within symbiodiniaceae (e.g. the genus symbiodinium). the association between symbiodinium and reef-building corals is widely known. 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. many extant dinoflagellates are parasites (here defined as organisms that eat their prey from the inside, i.e. endoparasites, 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: phototrophy, mixotrophy, and heterotrophy. phototrophs can be photoautotrophs 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). some dinoflagellates may feed on other organisms as predators or parasites. food inclusions contain bacteria, bluegreen algae, small dinoflagellates, 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