Chaetoceros pseudocurvisetus Mangin (1910: 350)

Bosak, Sunčica & Sarno, Diana, 2017, The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea, Phytotaxa 314 (1), pp. 1-44 : 32

Chaetoceros pseudocurvisetus Mangin (1910: 350) ( Figs 160–161 )

Bibliography: — Hustedt (1930), Cupp (1943), Fryxell (1978), Rines & Hargraves (1988), Hernández-Becerril (1996), Hernández-Becerril & Flores Granados (1998), Shevchenko et al. (2006), Kooistra et al. (2010).

Description: —a.a.: 15–35 μm; p.a.: 16–30 μm.

LM: —Cells are united in long, curved or helical chains ( Fig. 160 ). Cells are elliptical in valve view and rectangular in girdle view. In each cell there is a single lobed chloroplast ( Fig. 161 ). The valve face is concave with four protuberances situated along the valve margin, two per each side of the valve positioned close to the valve apices. Each protuberance fuses with the corresponding one on the sibling valve ( Fig. 161 ) forming a narrow oval aperture which is shorter than the cell apical axis ( Fig. 161 ). Intercalary setae originate from the valve corners and fuse immediately without basal part. In girdle view all setae are curved towards the same, convex side of the chain ( Fig. 160 ) while in valve view they are all bent to one side of the apical axis.

Distinctive features: —Chains curved in the pervalvar plane. Oval aperture narrower than in the very similar species C. curvisetus .

Figures

FIGURES 154–161. Chaetoceros messanensis, Chaetoceros protuberans, Chaetoceros pseudocurvisetus. Figs 154–157, 160–161: LM. Figs 158–159: SEM. Figs 154–155: Chaetoceros messanensis field material. 154) Complete chain with special forked intercalary setae. 155) Terminal part of the chain showing wide, hexagonal apertures and different orientation of the two terminal setae. Figs 156– 159: Chaetoceros protuberans field material. 156) Terminal part of a chain. 157) Sibling valves. 158) Sibling valves, note the poroids perforating the valve surface. 159) Detail of a seta. Figs 160–161: Chaetoceros pseudocurvisetus field material. 160) Middle part of the chain showing orientation of the setae. 161) Intercalary cells showing the short distinctive aperture (arrow). Scale bars: 154–156, 160=20 μm; 157, 161=10 μm; 158=5 μm; 159=0.5 μm.