LABORATORY STUDIES OF A GREEN NOCTILUCA FROM NEW GUINEA 1 , 2

SUMMARY A strain of Noctiluca miliaris Suriray, containing in the vacuole a motile green flagellate, was collected off the north shore of New Guinea and maintained in culture in autoclaved seawater or an enriched seawater medium. In light, this green Noctiluca survived for at least a month and divided, without added food; while in darkness the symbiotic flagellate disappeared and the Noctiluca died within a few days, unless the food organism Dunaliella tertiolecta was present. Long‐continued growth in light required the presence of Dunaliella , since the symbiotic flagellate was gradually lost under all the culture conditions assayed. All green Noctiluca assayed were luminescent. The light emitted per cell varied with the nutritional state of the host, and was as bright as a Japanese strain without symbionts when the Noctiluca was feeding on Dunaliella. In the absence of Dunaliella , the light emitted per Noctiluca depended on the light intensity in which cultures were maintained. The luminescent flash followed the same time course as that of other strains of Noctiluca without symbionts. No circadian rhythm of luminescence was present. Observations on both the growth and luminescence show that the flagellate symbiont contributes to the nutrition of the green Noctiluca. The symbiosis, however, is unstable in culture.