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B. Eukaryotic, but with unique chromosomes, at least in the dinoflagellates. They are bead-like, and seem to remain permanently condensed during interphase. Also there are no histones present.
C. Chloroplasts, if present, are golden brown to yellowish green. Pigments include chlorophyll a & c, a high proportion of carotenoids, and several characteristic xanthophylls.
D. Motile cells with two flagellae, usually dissimilar.
E. Cell walls, when present, consist of cellulose. There are two valves (hypotheca and epitheca) or a series of interlocking plates.
F. Food reserves are starch.
G. Reproduction is mostly asexual, but rarely, isogamous sexual reproduction may occur.
Typically there is a transverse or spiral groove, known as the girdle, and often, a longitudinal groove perpendicular to it. One flagellum is usually in the girdle, and the trailing flagellum is often in the longitudinal groove. Frequently an eyespot is present.
Feeding is diverse, with photosynthetic autotrophs predominating, but we also find saprotrophs, internal and external parasites, holozoic forms and even some zooxanthellae.
Most forms occur in warm ocean waters, of the imparting a red or yellow color to the water.
There are several bioluminescent forms, including Noctiluca, Peridinium, and Gymnodinium. They utilize luciferin and luciferinase.
Some forms are armored, having heavy plates as walls. These include Peridinium.
Economic and ecological significance includes playing a major role at the base of the food chain, and also being involved with red tides, etc. Gymnodinium and Gonyaulax especially are involved in the red tides. These organisms secrete neurotoxins, which cause significant fish die-offs, and may become air-borne, resulting in discomfort and distress to humans. The red tide problems may become worse as pathogenic bacteria build up un the dead fish, and deplete the oxygen in the water. This oxygen depletion can cause additional fish kills - referred to as dawn fish kills. These kills are the result of oxygen depletion, not toxins. This is the cause of the mahogany tides seen in the Chesapeake from time to time. Similarly, the dinoflagellate Ceratium may deplete the oxygen and cause die-offs referred to as black tides. This has occurred of the New Jersey Coast.
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