Chaetoceros protuberans 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 : 30-31

Chaetoceros protuberans Lauder (1864a: 79) ( Figs 156–159 )

References: — Hustedt (1930) (as Chaetoceros didymus var. protuberans ), Cupp (1943) (as Chaetoceros didymus var. protuberans ), Rines & Hargraves (1988) (as Chaetoceros didymus var. protuberans ), Lechuga-Devéze & Hernandez-Becerril (1988), Hernández-Becerril (1991b), Jensen & Moestrup (1998) (as Chaetoceros didymus var. protuberans ), Hernández-Becerril & Flores Granados (1998), Shevchenko et al. (2006), Kooistra et al. (2010), Lee et al. (2014b).

Synonym: — Chaetoceros didymus var. protuberans (Lauder) Gran & Yendo.

Morphometry: —a.a.: 13–24 μm; p.a.: 22–26 μm.

LM: —The cells are united in short and straight chains ( Fig. 156 ). Cells are elliptical in valve view and rectangular in girdle view with sharp and slightly drawn up corners. Valve face is slightly concave with a prominent hemispherical protuberance in the centre ( Fig. 156 ). The intercalary setae arise at the cell corners with a long basal part and cross over each other outside the chain margin ( Figs 156, 157 ). They diverge from the apical axis at a small angle in valve view, and in girdle view they are generally straight or slightly bent towards the chain end ( Fig. 156 ). The apertures are wide and constricted in the centre due to the presence of central protuberances on both sibling valves.

EM: —Valves are densely perforated with round small poroids lacking only on the central protuberance ( Fig. 158 ). A hyaline rim is present along the marginal ridge of the valve. The valve mantle is low with a slight constriction near its edge ( Fig. 158 ). The setae are generally four-sided in cross-section, with each side perforated with a single longitudinal line of elliptical poroids. Shark fin-shaped spines are arranged longitudinally on the ridges ( Fig. 159 ).

Distinctive features: —Valve face with a prominent hemispherical central protuberance. Absence of siliceous capilli present on the valves of the similar species C. didymus .

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.