Cymbella tropica var. tenuipunctata Krammer, 2002

Joh, Gyeongje, 2025, The seven species of the genus Cymbella (Bacillariophyta), previously unknown from the inland water of South Korea, Journal of Species Research 14 (1), pp. 6-19 : 15-18

Cymbella tropica var. tenuipunctata Krammer

( Figs. 64-72 )

Reference. Krammer, 2002. p. 61, pl. 49, figs. 12, 13.

Description. Valves slightly dorsiventral, semi-ellipticallanceolate in outline, dorsal margin strongly arched, ventral margin convex. Valves 30-37 μm long, 9-12 μm wide. Raphe lateral, reverse-lateral near the proximal ends and filiform near the distal ends. Striae 10-12 in 10 μm in the middle, areolae on a stria, 25-27 in 10 μm. Only one large stigma in the central parts of the ventral side.

Diagnoses. This variety differs from the nominate variety in areola density on a stria (25-28 vs. 21-24 in 10 μm) ( Krammer, 2002) and the ends of the valve weakly subrostrate, but thinner than that of the nominate variety.

Occurrence. This variety occurred together with C. tropica and mainly appeared in the Ian Stream in Sangju, and was also rarely found in some sections of the middle reaches of the Namhan River.

Among the seven species, significant variations in valve size were observed in three taxa: Cymbella compactiformis , C. neoleptoceros var. tenuistriata , and C. subcistula . The valve length of C. compactiformis ranged from 40 μm to 109 μm, with frequent occurrences of its early life cycle stages. This taxon, identified in China by Liu et al. (2018) and in Japan by Izumino et al. (2023), exhibit- ed noticeable size variations, with specimens from Korea showing a wider range. Variability in valve size and morphology has been well-documented in the genus Cymbella like C. cistula (Ehrenberg) Kirchner , C. microcephala Grunow , and C. delicatula Kützing. Specifically , C. cistula exhibited valve lengths ranging from 35 μm to 180 μm in Hustedt (1930). The valve length varies from 24 μm to 120 μm in Hufford and Collins (1972) and from 35 μm to 120 μm in Krammer and Lange-Bertalot (1986), exhibiting significant diversity in valve morphology. The extensive morphological variability led to the classification of numerous infraspecific taxa, resulting in challenges in accurate identification ( Fukushima et al., 1989). Some of these taxa have been further classified into distinct species. Krammer (2002), for instance, classified C. cistula into C. neocistula Krammer and C. subcistula , designating them as new species. The Cymbella subcistula reported in this study also displayed significant variability in valve dimensions.

Cymbella microcephala displays a wide range of variations in valve morphology, with differences in size and overall forms linked to its geographical distribution ( Ohtsuka et al., 1991). Hufford and Collins (1972) noted that in C. cistula population, the epiphytic assemblages were significantly smaller than those found on alternative substrates like stone or the bottom. However, this study did not find any differences based on substrates. In the indoor culture of freshwater diatoms, it has been reported that the size of the valve surface in xenic cultures is significantly larger, attributed to the presence of bacteria, compared to axenic cultures ( Windler et al., 2014).

On the contrary, C. maggiana , C. tropica var. tenuipunctata , and C. excisa showed limited variations in valve size. These three taxa were infrequently encountered in this survey, unlike the previously mentioned taxa. It is expected that populations with broader distribution areas and higher observation frequencies would display increased morphological diversity.

Figures

Figs. 64-72. Cymbella tropica var. tenuipunctata. 64-68. Valve view under LM. 69-72. Valve view under SEM. 69-71. The reverse-lateral deflection of the proximal raphe ends and filiform near the distal raphe ends (69, 70), slightly deflection of the central pores in the proximal ends of raphe (71). 70-72. One large stigma on the ventral side. 72. The internal view of the valve. Scale bars=10 μm (64-68); 4 μm (70, 72); 2 μm(69), 1μm (71).