Chaetoceros messanensis Castracane (1875: 32)

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

Chaetoceros messanensis Castracane (1875: 32) ( Figs 154–155 )

References: — Hustedt (1930), Cupp (1943), Evensen & Hasle (1975), Hernández-Becerril (1996), Hernández-Becerril & Flores Granados (1998), Shevchenko et al. (2006).

Synonyms: — Chaetoceros furca Cleve , Chaetoceros furca var. macroceros Schröder , Chaetoceros cornutus Leuduger-Fortmorel.

Morphometry: —a.a.: 10–37 μm; p.a.: 17–40 μm.

LM: —Cells are united in short, straight chains ( Fig. 154 ). Cells are rectangular in girdle view with sharp, drawn up valve corners which touch sibling cells. One chloroplast present per cell ( Fig. 154 ). The valve face is flat to slightly concave; the mantle is low without any constriction at its edge. Intercalary setae originate from the valve corners and fuse immediately without basal part. Apertures are very wide, elliptical to hexagonal ( Fig. 155 ). There are two types of intercalary setae: the thin common ones and thick special ones. Special setae are longer than the common ones, strongly silicified, fuse for about two thirds of their length and then separate again, strongly diverging into a thick and slightly undulated fork. Common setae are thin and in the girdle view equally diverged from the apical axis at an angle of 30–60°. Terminal setae are thin, strongly bent outwards from their point of origin and differ in orientation from each other, one being strongly bent toward the chain ( Figs 154, 155 ).

Distinctive feature: —Morphology of the intercalary special setae.

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.