Cocconeis scutellum Ehrenberg

Joh, Gyeongje, 2021, Distribution of the genus Cocconeis (Bacillariophyceae) along the Seogwipo coast of Jeju Island, South Korea, Phytotaxa 528 (3), pp. 149-179 : 166-167

21. Cocconeis scutellum Ehrenberg ( Figs 45–48 )

Basionym: Ehrenberg 1838, p. 194, pl. 14, fig. 8.

References: Poulin et al. 1984, p. 56, figs 43–48; Mizuno 1987, p. 592, figs 1–5, 6A–F; De Stefano et al. 2008, p. 508, figs 19–35.

Description: Valves elliptic-lanceolate to broadly elliptical, 13–31 μm long, 12–24 μm wide. SV: sternum narrow and linear, and central area not developed Transapical striae coarsely punctate, radiate towards the apices, 9–10 in 10 μm, uniseriate entirely, but bi- and tri-seriate near the mantle, areolae in striae coarsely circular, 9–12 in 10 μm of stria. RV: A narrow hyaline band in the submarginal area along the valve margin. Striae radiate, 10–13 in 10 μm, uniseriate, becoming biseriate on the mantle, areolae circular, 16–19 in 10 μm. Valvocopulae closed, having short fimbriae.

Remarks: Cocconeis scutellum is the most commonly reported in taxonomical and ecological research among the genus Cocconeis , but its morphological features have been neglected for a long time in the past. However, with the increase of SEM morphology, C. scutellum was recognized as a complex composed of many heterogeneous taxa rather than a single one (De Stephano et al. 2008). In the meantime, a lot of new taxa have been recently described as new species, and many specimens that have been reported as C. scutellum have been separated as new species (Riaux-Gobin et al. 2013). Therefore, the morphological boundary of the C. scutellum var. scutellum became very important, and it is not easy to identify the nominate variety.

The important feature of circumscribing C. scutellum from neighboring species is the poroid areolae on striae of SV, becoming biseriate or triseriate towards the mantle ( Mizuno 1987, De Stefano et al. 2008). Loculiferous bands in the margins of the RV, which is fimbriate valvocopulae, is visible.

Many frustules of the C. scutellum were also found in the Seogwipo coast, and the morphology of valves was very diverse and there were too many complex morphology and similarities, making it difficult to identify them. Although many images of light and electron microscopy were obtained, accurate identification was difficult. Only two species of C. scutellum and C. speciosa were extracted, and the rest were all set aside for later work.

This taxon is widespread and cosmopolitan along the coasts of marine and brackish waters, and has even been found in Antarctic regions ( Witkowski et al. 2000, De Stefano et al. 2008). In South Korea, it was reported frequently as planktons and periphytic off the coast (Lee 1995), as epiphytes on Zostera in Geoje Island ( Chung & Lee 2008), and as the epipsammic on the sand flat of the Nakdong River estuary ( Joh 2012). In this survey, common as epiphytes on seaweeds along the Seogwipo coast, particularly abundant in the lagoon (St. 3).

Figures

FIGURES 45–56. LM micrographs of Cocconeis species (3). Figs 45–48. Cocconeis scutellum, RV (Fig. 45) and SVs (Figs 46–48). Figs 49–52. C. shikinensis, SVs (Figs 49, 52) and RVs (Figs 50, 51). Figs 53–56. C. schmidtii, RVs (Figs 54, 56) and SVs (Figs 53, 55). Scale bar = 10 μm (Figs 45–56).