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 .

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