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Dinocyst

Dinocysts or dinoflagellate cysts are typically 15 to 100 µm in diameter and produced by around 15–20% of living dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic-walled dinocysts are often resistant and made out of dinosporin. There are also calcareous dinoflagellate cysts and siliceous dinoflagellate cysts.Many books provide overviews on dinocysts. Dinocysts or dinoflagellate cysts are typically 15 to 100 µm in diameter and produced by around 15–20% of living dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic-walled dinocysts are often resistant and made out of dinosporin. There are also calcareous dinoflagellate cysts and siliceous dinoflagellate cysts.Many books provide overviews on dinocysts. The first person to recognize fossil dinoflagellates was Christian Gottfried Ehrenberg, who reported his discovery in a paper presented to the Berlin Academy of Sciences in July 1836. He had observed clearly tabulate dinoflagellates in thin flakes of Cretaceous flint and considered those dinoflagellates to have been silicified. Along with them, and of comparable size, were spheroidal to ovoidal bodies bearing an array of spines or tubes of variable character. Ehrenberg interpreted these as being originally siliceous and thought them to be desmids (freshwater conjugating algae), placing them within his own Recent desmid genus Xanthidium. Though summaries of Ehrenberg's work appeared earlier, it was not published in full until 1837 or 1838; the date is uncertain. A first relation between dinoflagellate thecae and cysts was made through morphological comparison of both by Bill Evitt and Susan E. Davidson. Further evidence came from detailed culture studies of dinoflagellate cysts by David Wall and Barrie Dale at Woods Hole Oceanographic Institution in the sixties. Ontologically, the term cyst can apply to (1) a temporary resting state (pellicle, temporary or ecdysal cyst), (2) a dormant zygote (resting cysts or hypnozygotes) or (3) a coccoid condition in which the cells are still photosynthetically active. For example for this last special case, all cysts described from species of the order Phytodiniales (e.g. Cystodinium, Stylodinium, Hypnodinium, Tetradinium, Dinococcus, Gloeodinium), are coccoid stages. Digestive cyst or digestion cysts denote pellicle cysts formed after feeding by phagocytosis as in Katodinium fungiforme . Division cysts refer to non-motile division stages wherein asexual reproduction takes place through division. These are not pellicle or resting cysts since they are not dormant. Similarly, palmelloid or mucilage stages are not pellicle or resting cysts, but stages in which the monad loses its flagella and becomes enveloped in multilayered mucilage wherein division takes place. Dinoflagellate cysts described in the literature have been linked to a particular motile stage through morphological similarities and/or co-occurrence in the same population/culture or through the technique of establishing the so-called cyst-theca relation by incubation of the cysts. Geologists use a cyst-based taxonomy, whilst biologists use a motile-stage based taxonomy. Therefore cysts can have different names than the corresponding motile stages. Living cysts can be easily isolated from the sediment using sodium polytungstate, a heavy liquid. Another method, rarely used, uses a sucrose gradient. Recent times have brought about the possibility to get molecular sequences from single cysts or single cells. The proportion of cyst-forming species for marine dinoflagellates is between 15 and 20% and for freshwater dinoflagellates 24%.The tabulation of the Dinoflagellate is sometimes mirrored in the tabulation (previously called paratabulation) of the dinocyst, allowing species to be deduced from the cyst.It has previously been suggested that morphological characters from the cyst stage may be phylogenetically important in marine species and this may to an even greater extent be the case for freshwater dinoflagellates, confirmed by new observations and recently reviewed.Several books document general cyst taxonomy.There are few guides for determination of marine Quaternary dinocysts. Many new species are still being described for the Neogene, which covers the Miocene, the Pliocene and the Quaternary, which covers the Pleistocene and recent. Quaternary dinocysts are typically between 15 and 100 µm in diameter. One of the smallest recent cysts is the cyst of Pentapharsodinium dalei, which can be as small as 19 µm in length. One of the largest recent cysts is the cyst of Protoperidinium latissimum, which can be as large as 100 µm in length. The walls of organic-walled dinocysts are composed of the resistant biopolymer called dinosporin. This organic compound has similarities to sporopollenin, but is unique to dinoflagellates.

[ "Palynology", "Dinoflagellate", "Spiniferites elongatus", "Selenopemphix", "Pentapharsodinium dalei", "Islandinium minutum", "Pyxidinopsis" ]
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