| Abstract: | Resting cyst formation of Eutreptiella gymnastica Throndsen was observed during a mesocosm experiment, where nutrient enrichment had induced almost a unialgal bloom. Cells and resting cysts of E. gymnastica were examined in scanning (SEM) and transmission electron microscopy (TEM) and light microscopy. Mature cysts were spherical, with a smooth thick mucilaginous cover that appeared layered when observed with the TEM. Intermediate forms were spherical and lacking flagella and a mucilaginous cover; the euglenoid pellicular striation and canal opening were easily visible. The volume of these intermediate spherical cells and mature cysts was estimated to have increased threefold compared to flagellated cells and contained many paramylon grains. When the cells were grazed by zooplankton, the paramylon grains passed the gut intact and were packed into fecal pellets. Intact undigested paramylon grains were observed in SEM after the breaking up of the pellets. |
