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P. bahamense, G. polyedra, and P. lunula exhibit interspecies differences in stimulable and spontaneous bioluminescence. For each species the total number of photons that can be emitted upon mechanical stimulation is a constant, regardless of the time during scotophase at which stimulation occurs. Ratios of stimulable bioluminescence per organism during scotophase and photophase are as high as 950:1 for laboratory cultures and have been observed as high as 4000: 1 for natural populations of P. bahamense. Spontaneous emission in darkness shows flashing as well as low-level continuous emission. Natural populations of P. bahamense, placed in darkness during natural photophase, exhibit a dual character to their stimulable bioluminescence. Mechanical stimulation techniques are described for rapid and reproducible stimulation of bioluminescence.

In both photosynthetic (Pyrodinium bahamense, Gonyaulax polyedra, Pyrocystis Iunula, P. noctiluca, P. fusiformis) and nonphotosynthetic (Noctiluca miliaris) bioluminescent dinoflagellates chemical stimulation can by-pass mechanical stimulation. The effective ions are Ca++, K+, NH4+ and H+. Other chemicals found effective are those implicated in Ca++ transport or binding. There are interspecies differences in degrees of mechanical and chemical stimulability. Photoinhibition of mechanical stimulability is the result of two effects, the first a reduction in total bioluminescence potential and the second a decrease in mechanical stimulability resulting experimentally in a decreased rate of light emission. This latter effect can be reversed with Ca++ ions. Chemicals which bind Ca++ or displace Ca++ can mimic the effects of photoinhibition. The chemical inhibition of mechanical stimulability is also reversed by Ca++ ions. A scheme is proposed which is consistent for all species examined.

The bioluminescent, photosynthetic, tropical marinc dinoflagellate Pyrodinium bahamense occurs in persistent high concentrations in Oyster Bay, Jamaica, W. I., although mean tidal flushing rates determined by dye-tracer techniques would predict their disappearance. As a result of a unique temporal sequence of positive phototaxis and the differential movement of diurnal wind-driven water layers of different densities, there is a daily transfer of P. bahumense into the eastern shallows of the bay where flushing rates are minimal, reducing the effect of the mean bay dilution. A second phototaxis-dependent mechanism in the eastern shallow results in zones of high concentration containing up to 10,000,000 P. buhamense per liter. This latter mechanism can explain the production of red water outbreaks in coastal waters. Nitrogen and phosphorus levels observed are consistent with both mechanisms.

Germination experiments demonstrate that the "hystrichosphere" called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. The morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is concluded that Pyrodinium is closely related to Gonyaulax but worthy of retention as a discrete genus. The geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and it is suggested that additional pyrodinioid dinoflagellates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyrodinium.

The morphology and asexual cycle of the luminescent armoured dinoflagellate, Pyrodinium bahamense Plate, were examined in situ and in vitro. Several previously unreported aspects of the cycle are described. Attempts to induce the formation of these alternate life stages by imposing new conditions were unsuccessful.

With the same extraction conditions used for Gonyaulax polyedra, soluble and particulate bioluminescence can be isolated from two additional species, Pyrodinium bahamense and Pyrocystis lunula. We have been able, for all three species, to dissociate soluble luciferin and luciferase from the particulate system. Luciferin can be incorporated into both reacted and unreacted particulate systems.