Skeletonema grevillei Sarno et Zingone

Hernández-Becerril, David U., 2023, Further studies on the species diversity of the marine planktonic diatom genus Skeletonema (Bacillariophyta) in the Mexican Pacific, Phytotaxa 607 (3), pp. 182-196 : 187

Skeletonema grevillei Sarno et Zingone

Figs 12–17

References: Zingone et al. 2005, p. 144, figs 5 A–F, 6 A–I; Sarno et al. 2007, p. 162, figs 2 A–J; Naik et al. 2010, p. 291, figs 3–6; Gu et al. 2012, p. 254, figs 15–17; Bužančić et al. 2017, p. 195, figs 2–5.

Description: Chains are relatively thin, delicate, mostly long (2–9 cells per chain, usually more than 6) and straight to slightly curved ( Fig. 12 ). Usually there are two chloroplasts per cell ( Fig. 12 ). Valves are flat to slightly convex, with a relatively high valve mantle ( Figs 13–16 ). Most specimens show siliceous ridges, sometimes poorly developed, dividing valve face and mantle ( Figs 13, 15 , small arrows). Additional ridges are also found at the bases of the fultoportulae ( Figs 14, 16 , small arrows). The valves have very irregular areolae with rectangular, polyedric or elongate areolae ( Figs 16, 17 ). Details of the cingular bands were not observed.

The fultoportulae are open throughout them ( Figs 13–16 ), and the TF’s have their tips irregularly truncated ( Figs 13, 15, 16 ). Each IF fuses to one of the sibling valve ( Figs 13, 14 ). Three to four satellite pores surround each fultoportula ( Fig. 17 , arrows). The TR’s are marginal ( Figs 13, 16 , arrows), and have a long tube, with an inflated tip ( Figs 13, 15, 16 , arrows), whereas the IR is almost marginal, but very short ( Fig. 14 , arrow).

Measurements: cell diameter 3.4–5.8 μm, areolae density 33–51 in 10 μm ( Table 1 ).

Figures

FIGURES 12–17. Skeletonema grevillei, LM (12), SEM (13–16) and TEM (17). Fig. 12. A rather long chain of 8 cells, some of them dividing, containing two chloroplasts per cell. Fig. 13. Terminal part of a chain showing terminal and intercalary valves, siliceous ridges (small arrows) between face and mantle at the terminal valve, TF’s, one TR (arrow), and broken IF’s. Fig. 14. Intercalary valves with IF’s fusing to those of sibling valve in 1:1 junction type, a short IR (arrow), and siliceous ridges (small arrows) around bases of IF’s. Fig. 15. Terminal valve with fultoportulae (TF’s) irregularly truncated, a marginal rimoportula (arrow), and siliceous ridges (small arrows) dividing valve face and mantle.Fig. 16.Another terminal valve showing details of the areolae, siliceous ridges (small arrows) around bases of the TF’s, and a marginal rimoportula with slightly inflated tip (arrow). Fig. 17. Details of the three to four satellite pores surrounding each fultoportula (arrows).