The planktonic diatom genus Chaetoceros Ehrenberg (Bacillariophyta) from the Adriatic Sea Author Bosak, Sunčica University of Zagreb, Faculty of Science, Department of Biology, Rooseveltov trg 6, HR- 10000 Zagreb, Croatia Author Sarno, Diana Stazione Zoologica Anton Dohrn, Department of Integrative Marine Ecology, Villa Comunale, 80121 Naples, Italy text Phytotaxa 2017 2017-07-21 314 1 1 44 http://dx.doi.org/10.11646/phytotaxa.314.1.1 journal article 10.11646/phytotaxa.314.1.1 1179-3163 13700770 Chaetoceros diversus Cleve (1873: 9) ( Figs 133–141 ) References: — Hustedt (1930) , Cupp (1943) , Hernández-Becerril (1996) , Moreno Ruiz et al . (1993) , Hernández-Becerril & Flores Granados (1998) , Shevchenko et al . (2006) , Lee et al. (2014a) . Synonyms: — Chaetoceros laevis Leuduger-Fortmorel , Chaetoceros rudis Leuduger-Fortmorel , Chaetoceros diversus var. tenuis Cleve , Chaetoceros diversus var. mediterranea Schröder. Morphometry: —a.a.: 7–14 μm; p.a.: 6–11 μm. LM: —Cells are united in short straight chains of 3–9 cells ( Fig. 133 ). In valve view cells are generally circular, in girdle view rectangular with sharp corners. One chloroplast is present per cell ( Fig. 134 ). The setae originate at the valve corners and fuse immediately at the chain margin without a basal part. The apertures are slit-shaped and very narrow or almost absent ( Fig. 134 ). There are two types of intercalary setae: the common ones and special ones ( Fig. 133 ) showing a different thickness and orientation. Special setae diverge at an angle of about 45° from the chain axis and then curve towards the terminal part of the chain. They become thicker after some length and then taper again towards their ends. Terminal setae extend almost parallel to the chain axis diverging in a U-shaped curve ( Fig. 133 ). All setae of a chain lie in the apical plane. EM: —The valve has a central annulus from which a weak pattern of radiating costae branches dichotomously towards the valve margin ( Fig. 135 ). The area between costae is irregularly perforated with densely scattered small poroids. Valve is face flat or slightly convex, and the mantle is high with a slight constriction near the edge ( Fig. 136 ). Between the valve face and the mantle in most cases there is no discernible marginal ridge, and only sometimes the extensions of the hyaline rim are fused between sibling cells at each edge of the aperture ( Fig. 136 ). Terminal cells have a labiate-shaped rimoportula with a small projection on the outside ( Figs 137, 138 ) Special setae are strongly silicified and ornamented with thick shark fin-shaped spines ( Fig. 139 ). Common intercalary setae have four to five longitudinal or slightly spiral rows of rectangular poroids as well as spines spirally arranged around the seta ( Fig. 140 ). Girdle bands are ornamented with transverse parallel ribs ( Fig. 141 ). Distinctive features: —General shape of the chain, cells with very sharp corners and narrow apertures, setae widely diverging in apical plane, with special thicker intercalary setae.