Chaetoceros eibenii Grunow

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 9

Chaetoceros eibenii Grunow in Van Heurck (1882: pl. LXXXII) ( Figs 16–23 )

References:— Hustedt (1930), Cupp (1943), Von Stosch et al. (1973), Koch & Rivera (1984), Rines & Hargraves (1988), Jensen & Moestrup (1998), Lee et al. (2014b).

Synonym: — Chaetoceros paradoxus var. eibenii Grunow.

Morphometry: —a.a.: 13–42 μm; p.a.: 11–38 μm.

LM: —Cells united into robust, straight and long chains ( Fig. 16 ). In girdle view cells are rectangular with sharp valve corners ( Fig. 17 ). Cells and setae contain numerous chloroplasts. The valve surface is slightly concave with a spine-like central process visible on every valve ( Fig. 17 ). The valve mantle is low. Setae originate inside the valve margin and have a relatively short basal part ( Fig. 17 ).

EM: —The valves are very heavily silicified and perforated with poroids irregularly scattered over the valve face, setae bases, and mantle. In valve view, one seta is oriented parallel to the apical plane and the other one diverges from it at approximately 90° angle ( Fig. 18 ). However, the divergence angle can be quite variable. The marginal ridge is often ornamented with a strongly silicified low hyaline rim with an uneven edge ( Fig. 18 ). A central rimoportula is present in each valve. It appears as a simple hole from the inside, and brings a flattened or round tube with a tapering tip on the outside of the valve ( Figs 18–19 ). The setae are six-sided ( Fig. 22 ) with a row of very strong, shark fin-shaped spines on each ridge ( Fig. 23 ). The setae sides are ornamented by relatively thick and distinct transverse costae interspaced by less silicified areas, which are perforated by numerous very small poroids, sometimes arranged in rows close to costae but otherwise irregularly scattered over the hyaline area ( Figs 20–21 ). One larger round pore is present near the ridge and close to the costa on either sides of the side-wall, at an interval of 4–8 costae ( Fig. 21 ).

Distinctive features: —Hexagonal apertures, a spine-like rimoportula process visible in every valve. Six-sided setae, ornamented with thick costae interspaced by numerous very small poroids.

Figures

FIGURES 13–23. Chaetoceros densus, Chaetoceros eibenii. Figs 13, 14, 16: LM. Figs 15, 20, 21: TEM. Figs 17–19, 22–23: SEM. Figs 13–15: Chaetoceros densus field material. 13) Terminal part of a chain. 14) Sibling valves in valve view. 15) Detail of a seta. Figs 16, 18–22: Chaetoceros eibenii culture material, strain PMFH1. 16) Complete chain of two cells. Fig. 17: Chaetoceros eibenii field material. 17) Terminal part of a chain showing wide hexagonal apertures and a rimoportula visible on every valve. 18) Valve view of sibling valves showing setae divergence. 19) External view of the valve with rimoportula and hyaline rim on the marginal ridge (arrows). 20) Detail of the seta. 21) Detail of a broken seta showing the ornamentation pattern of the side wall. The larger round poroid is indicated by an arrow. 22) Hexagonal cross-section of the seta. 23) Seta tip. Scale bars: 16= 50 μm; 13, 14, 17=10 μm; 18, 19=5 μm; 15, 20–23=1 μm.