Chaetoceros coarctatus Lauder (1864a: 79)

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 7

Chaetoceros coarctatus Lauder (1864a: 79) ( Figs 2, 3 )

References:— Hustedt (1930), Cupp (1943), Hernández-Becerril (1991a), Nagasawa and Warren (1996), Lee et al. (2014b).

Synonyms: — Chaetoceros borealis var. rudis Cleve , Chaetoceros rudis Cleve , Chaetoceros validum Grunow in Cleve & Möller.

Morphometry: —apical axis (a.a.): 26–36 μm; pervalvar axis (p.a.): 42–63 μm.

LM: —The cells form heteropolar , straight, robust and long chains. Heavily silicified cells are rectangular in girdle view with the diagonally cut valve corners ( Fig. 2 ). Numerous small chloroplasts are present in the cell body and the setae ( Fig. 3 ). The advalvar mantle edge is constricted, mantle is high and equidimensional or smaller than the girdle. Valve surface is flat, setae arise within the valve margin with a very short, and practically non-existent basal part therefore the apertures are extremely narrow and often the valve faces of sibling cells touch each other ( Fig 2 ). The sibling setae cross each other near the chain edge and after crossing point diverge at an angle of about 30–45° from the apical plane. All setae are thick, coarse and curved towards the posterior end of the chain ( Fig. 3 ). No morphologically distinct type of terminal or intercalary setae was observed ( Fig. 3 ).

Distinctive features: —Robust chains, large cells with constricted valve edge, very narrow apertures. All setae curved towards one side of the chain. Chains commonly found with epizoic ciliate Vorticella sp. attached to the cells, sometimes in large numbers.

Figures

FIGURES 2–12. Chaetoceros coarctatus, Chaetoceros dadayi, Chaetoceros danicus. Figs 2–6: LM. Figs 7, 9–12: TEM. Fig. 8: SEM. Figs 2–3: Chaetoceros coarctatus field material. 2) Middle part of a chain, note the narrow apertures and attached ciliate cells. 3) Terminal part of a chain showing the orientation of the setae. Arrows indicate plastids within the setae. Fig. 4: Chaetoceros dadayi field material. Complete chain with the attached tininnid lorica. Note the characteristic orientation of intercalary setae. Figs 5–12: Chaetoceros danicus culture material, strain PMFDA1. 5) Cell in valve view, note the cross orientation of the setae. 6) Chain of two cells in girdle view. 7) Valve view showing the fine structure. 8) Internal view of the valve. 9) Fine structure of the two overlaid valves with the siliceous thickenings on the valve margin (arrow) 10) Detail of a seta. 11) Single side of the seta with arrowhead spines and poroids arranged in a grid pattern. 12) Detail of a girdle band. Scale bars: 3=50 μm; 2, 4, 5=20 μm; 6=10 μm; 7, 9=5 μm; 8=2 μm; 10–12=1 μm.