Chaetoceros constrictus Gran (1897: 17)

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 20

Chaetoceros constrictus Gran (1897: 17) ( Figs 79–82 )

References:— Hustedt (1930), Cupp (1943), Rines & Hargraves (1988), Hernández-Becerril (1996), Jensen & Moestrup (1998), Hernández-Becerril & Flores Granados (1998), Berard-Therriault et al. (1999), Shevchenko et al. (2006), Lee et al. (2014a).

Morphometry: —a.a.: 5–18 μm; p.a.: 7–17 μm.

LM:—Cells are united in very straight and usually short chains ( Fig. 79 ). The valve surface is concave and the valve corners are sharp and drawn up, touching between sibling valves ( Fig. 81 ). The aperture is quite large and distinctively elliptically shaped ( Figs 79, 81 ). Valve mantle is high with a distinct constriction near the margin ( Fig. 81 ). Intercalary setae are long and rigid; originate from the valve apices and immediately cross each other at the chain margin without the basal part. In girdle view they are usually proximally perpendicular towards the chain axis and distally curved ( Fig. 79 ). Terminal setae are usually characteristically oriented, long and straight, extending parallel to the chain axis and sometimes crossing each other distally ( Fig. 79 ).

EM: —The valve face is ornamented with numerous small spines which are more pronounced in terminal valves ( Fig. 82 ). The marginal ridge has a distinct hyaline rim ( Fig. 82 ). A rimoportula, bearing an external short, flattened and wide tube, is present only in terminal valves ( Fig. 82 ). Setae are quadrangular in cross-section, perforated with longitudinal rows of small slit-shaped poroids and small spines ( Fig. 80 ).

Distinctive features: —Valve mantle markedly constricted near the advalvar margin, observable in LM as a marked constriction near the girdle. Intercalary setae long, straight and rigid, terminal setae extending parallel to the chain axis sometimes distally crossing each other. Valve face ornamented with many small spines.

Figures

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.