Chaetoceros anastomosans Grunow

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 16-17

Chaetoceros anastomosans Grunow in Van Heurck (1882: pl. 82) ( Figs 54–62 )

References:— Hustedt (1930), Cupp (1943), Hernández-Becerril & Flores Granados (1998), Hernández-Becerril & Aké-Castillo (2001), Shevchenko et al. (2006), Lee et al. (2014b).

Synonyms: — Chaetoceros anastomosans var. speciosa Schutt , Chaetoceros anastomosans var. genuina Cleve-Euler , Chaetoceros externus Gran , Chaetoceros anastomosans var. externa (Gran) Hustedt.

Morphometry: —a.a.: 8–10 μm; p.a.: 5–14 μm.

LM: —The cells are united in usually long, straight to slightly curved chains ( Fig. 54 ). In girdle view cells are nearly squared to rectangular with the rounded valve corners ( Fig. 55 ). There are two chloroplasts per cell, positioned within each valve ( Fig. 55 ). The valve face is flat or slightly convex. Valve mantle is low with a very slight constriction near the margin. The thin and delicate setae originate from the valve corners. Intercalary setae generally bend at right angles or extend perpendicular to the chain axis. In the valve view they diverge almost equally at an angle of ca. 30–45° from the apical plane ( Fig. 56 ). Cells are connected by a siliceous cross-bridge of variable length which joins sibling setae at a short distance from the valves ( Fig. 55 ). The sibling setae do not cross and form wide apertures that have an unusual, octagonal shape, elongated in the apical direction ( Fig. 55 ). The terminal setae diverge obliquely towards the chain axis becoming almost parallel with it, forming U-shape ( Fig. 54 ).

EM: —The valves have a relatively large central annulus from which dichotomously branching costae radiate toward the margins ( Figs 57, 58 ). The marginal ridge is ornamented with a hyaline rim often extended in short projections in the pervalvar direction ( Figs 56, 57 ). A slit-shaped rimoportula is present only in terminal valves ( Fig. 59 ). Girdle bands are narrow and ornamented with alternating transverse hyaline striae and costae ( Fig. 60 ). The setae are circular in cross-section, ornamented with minute arrowhead-shaped spines and poroids running spirally throughout. Additional elongated poroids are randomly distributed along the setae length ( Fig. 61 ). The cross-bridge appears as a hyaline tube with a swelling in the central part, fused on the setae surface ( Figs 56, 61 ).

Distinctive features: —Cells connected in chains by a cross-bridge which joins sibling setae. Absence of setae crossing.

Figures

FIGURES 54–62. Chaetoceros anastomosans. Culture material. Figs 54–55, 61: strain PMFAN2. Figs 56–60, 62: strain PMFAN1. Figs 54, 55: LM. Fig. 56: SEM. Figs 57–62: TEM. 54) A chain. 55) Middle part of a chain showing a cross-bridge connection between sibling cells and the wide octagonal aperture. 56) Sibling valves in valve view. 57) Cell in girdle view showing the hyaline rim at the mantle ridge (arrow). 58) Valve face showing the central annulus and dichotomously branching costae. 59) Slit-shaped rimoportula on a terminal valve. 60) Part of the girdle. 61) Cross-bridge between sibling setae.Arrow shows the elongated poroid perforating the setae. 62) Detail of a seta. Scale bars: 54=20 μm; 55=10 μm; 57, 60–61=2 μm; 56, 58=1 μm; 59, 62=0.5 μm.