Chaetoceros lauderi Ralfs

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 28-30

Chaetoceros lauderi Ralfs in Lauder (1864a: 77) ( Figs 142–153 )

References: — Hustedt (1930), Cupp (1943), Hargraves (1979), Rines & Hargraves (1988), Hernández-Becerril & Flores Granados (1998), Jensen & Moestrup (1998), Sunesen et al. (2008), Kooistra et al. (2010), Ishii et al. (2011).

Synonyms: — Chaetoceros weissflogii Schütt.

Morphometry: —a.a.: 15–39 μm; p.a.: 27–63 μm.

LM: —Cells are united into long straight chains which are slightly twisted around the chain axis ( Fig. 142 ). In valve view cells are circular to elliptical, in girdle view rectangular with sharp corners and pervalvar axis generally longer than the apical axis ( Fig. 143 ). There are numerous (25–45) small chloroplasts present in each cell ( Fig. 143 ). The valve face is flat. The mantle is low without constriction at its edge while the girdle is usually very broad. Intercalary setae emerge from the corners of the valves, fuse without a basal part and immediately diverge in different directions. Apertures are very narrow and slit-like ( Fig. 143 ). Setae are generally straight, extending perpendicular to the chain axis, with some of them curving towards either end of the chain ( Fig. 142 ). In valve view setae diverge from the apical plane at an angle of 30–40°; in some cases one seta is parallel with the apical plane and the other is more or less perpendicular. Terminal setae are morphologically similar to intercalary ones, strongly diverging in a broad Ushaped curve ( Fig. 142 ).

EM: —The valve face is ornamented with densely and irregularly distributed anastomosing costae radiating from a relatively large central annulus ( Figs 144, 145 ) and becoming parallel on the valve mantle ( Fig. 146 ). The area between costae is hyaline. The marginal ridge is often ornamented with a very low hyaline rim ( Fig. 147 ). Terminal valves possess a slit-shaped rimoportula ( Figs 146, 148 ) with an external wide flattened tube ( Fig. 147 ). Setae are circular in cross-section, ornamented with small poroids and shark fin-shaped spines arranged in a spiral pattern ( Fig. 149 ). The girdle bands have parallel transverse ribs alternating with less silicified areas perforated by irregularly distributed small poroids ( Fig. 150 ). The resting spores are ornamented with long spines on their primary valve and few long thing capilli on the secondary valve. ( Fig 151 ). The capitate primary valve of the resting spore is constricted at its base and spines which are either completely straight or sharply bent near the tip ( Fig. 152 ). Secondary valve is flat to vaulted, either with smooth surface or ornamented with thin and very long hair-like spines (capilli) which are commonly present in a form of a single ring on the mantle advalvar margin ( Fig. 153 ).

Distinctive features: —Elongated cells, very narrow and almost non-existent apertures. Chains slightly twisted around the axis and setae diverging in all directions. Resting spores with long spines on the capitate primary valve and ring of long capilli around the secondary valve mantle.

Figures

FIGURES 142–153. Chaetoceros lauderi culture material, strain PMFL1. Figs 142–143, 151: LM. Figs 144–146, 148, 150: TEM. Figs 147, 149, 152–153: SEM. 142) Complete chain showing setae orientation. 143) Intercalary cells with numerous chloroplasts. 144) Two overlapped sibling valves showing valve ornamentation.145) Detail of the valve with central annulus and anastomosing ribs.146) Terminal valve with slit-like rimoportula (arrow). Note the parallel ribs on the valve mantle. 147) Terminal valve with external flattened tube of the rimoportula. Note the low hyaline rim on the marginal ridge. 148) Detail of the terminal valve with the slit-like rimoportula. 149) Detail of a seta. 150) Detail of the girdle band. 151) Resting spore. Note the single ring of puncta on the advalvar margin of the secondary valve mantle (arrow). 152) Primary valve of the resting spore. 153) Secondary valve of the resting spore with the single ring of puncta on the advalvar mantle margin. Scale bars: 142=50 μm; 143=20 μm; 151–153=10 μm; 144, 146–147=5 μm; 145, 148–150=1 μm.