Dinoflagellates (meaning whirling whips) are second only to the diatoms as primary producers in the world's oceans. They are single-celled organisms generally between 20 and 150 |im in maximum diameter, with both plant and animal characteristics. Most dinoflagellates are distinguished by a dinokaryon, a special form of eukaryote nucleus. Their carotenoid pigments dinox-anthin and peridinin give to these organisms flame-like colours and produce 'red tides' when populations bloom. Many living dinoflagellates are also bioluminescent.
The majority of dinoflagellates exhibit alternation of generations in the life cycle and bear two flagella for propulsion. Motile (theca) cells are equipped with one longitudinal whip-like and one transverse ribbon-like flagellum for propulsion, have a prominent nucleus and a sculptured cell wall (Fig. 10.1). Both heterotrophic and autotrophic modes of nutrition occur, although the latter predominate. Dinoflagellates have formed an important part of oceanic phytoplankton since at least mid-Mesozoic times. Although motile cells are abundant and wide ranging, it is the resistant resting cyst which leaves a fossil record. Dinoflagellate cysts have proved to be valuable tools in biostratigra-phy and are also important in palaeoecology, palaeo-climatology and evolutionary palaeontology.
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