FIGURES 72–82. Chaetoceros circinalis, Chaetoceros constrictus. Figs 72–73, 79, 81: LM. Figs 74–75, 77–78, 80, 82: SEM. Fig 76: TEM. Figs 72–78 Chaetoceros circinalis culture material, strain PMFG4. 72) A complete chain and a single cell showing the curvature of the setae. 73) Valve view of a cell showing the characteristic curvature of the setae. 74) Two sibling valves with partially fused hyaline rim at the aperture edge (arrows). 75) Terminal valve with wide flattened tube-like rimoportula process and short capilli on the valve surface. 76) Terminal valve with wide flattened tube-like rimoportula process. 77) Detail of proximal part of intercalary setae showing elongated poroids (arrow). 78) Detail of a seta. Figs 79–82 Chaetoceros constrictus field material. 79) Short chain showing orientation of the setae. 80) Detail of a seta. 81) Intercalary cells in girdle view showing the distinct constrictions near the mantle margin (arrows). 82) Terminal cell showing external flattened tube of the rimoportula, the small spines covering the valve surface and longitudinal groove near the mantle edge. Scale bars: 79=20 μm; 72–73, 81–82=10 μm; 74–78, 80=1 μm.