Cysts of the toxic red-tide dinoflagellateGonyaulax excavata(Braarud) Balech from Oslofjorden, Norway

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Abstract
Gonyaulax excavata was cultured from, resting cysts isolated from bottom sediments in Oslofjorden, the type locality. Resting cysts were elongate-ovoid with thick smooth walls surrounded by gelatinous material incorporating detritus; contents typically included starch grains, oil globules, and a conspicuous red-pigmented body. A resting period seems to be mandatory, and cysts are suggested to act as ‘seed beds’ for some toxic blooms. Other non-motile cells (temporary cysts) were formed in cultures, cooled from 15° C to less than 5° C. These had thinner walls and lacked gelatinous cover and typical cell contents of resting cysts. They quickly reestablished motile cells when returned to 15° C. Cultured motile cells were toxic to mice, bioluminescent, and consistently lacking ventral pores, in accordance with recent suggestions that these are specific criteria. Resting cyst morphology suggests a possible systematic relationship between G. excavata and Pyrophacus horologium.