Cocconeis convexa Giffen

5. Cocconeis convexa Giffen (Figs 42–44, 100–102)

Basionym: Giffen 1967, p. 257, figs 26–28.

References: Witkowski et al. 2000, p. 104, pl. 37, figs 5, 6, pl. 41, figs 1–4; Suzuki 2001, p. 60, figs 1–35; Riaux-Gobin et al. 2011, p. 22, pl. 3, figs 1–5, pl. 32, figs 1–7.

Description: Valves broadly elliptical to almost rhombic, 16–25 μm long, 12–18 μm wide. SV: sternum narrow and linear, and central area not developed. Transapical striae parallel at middle, strongly radiate towards the apices, and interrupted by many slightly undulate hyaline lines, 37–41 in 10 μm. RV: raphe straight, the central ends of raphe slightly curved to the opposite directions, the terminal ends of the raphe distant from the apices without areolation and sternum narrow. Central area expanded transversely to less than half the hemivalve, and central nodule between the central raphe ends thickened. Under the LM, only the thickened central nodule highlighted, making the central area more narrow than it really is. Transapical striae parallel in the middle, strongly radiate towards the apices, 26–31 in 10 μm of stria, often 1–2 striae in the middle of one side of the valve particularly short.

Remarks: Cocconeis convexa is pantropical, and described from the Pacific and Indian Oceans (Witkowski et al. 2000), Guam in the western Pacific Ocean (Navarro & Lobban 2009), Réunion and Rodrigues in the western Indian Ocean (Riaux-Gobin et al. 2011), and Tahiti and Tuamotu Archipelago of the southern Pacific Ocean (Riaux-Gobin et al. 2015). The species has been reported from the coasts of Japan (Suzuki 2001), Argentina (Sar et al. 2003), Mexico (Siqueiros-Beltrones & Argumedo-Hernández 2015). In South Korea, it was already reported in the coast of Jeju Island (Kim et al. 2017), and in this survey, was found frequently as epiphytes on seaweeds along the Seogwipo coast.