Cymbella neoleptoceros var. tenuistriata 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 : 12-14

Cymbella neoleptoceros var. tenuistriata Krammer

( Figs. 44-53)

Reference. Krammer, 2002. p. 135, pl. 160, figs. 1-6.

Description. Valves slightly dorsiventral, semi-lanceolate in larger forms or semi-rhomboidal in smaller ones in outline, ventral margin convex in small forms and tumid in the middle portion in large forms. Valves 18-46 μm long, 7-10 μm wide. Raphe lateral, filiform far from the proximal ends and from distal ends. Striae narrower than the interstrial width in the central parts of the valve, 8-11 in 10 μm in the middle, areolae on a stria lineate, 20-23 in 10 μm. Stigma lacking.

Diagnoses. First of all, this variety contrasts with the nominate variety, C. neoleptoceros , in terms of the width of the striae and the costae between the striae. The variety is differentiated in that the interstriae are broader than

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striae, and the nominate is differentiated in that the striae are wider. It is clear in SEM images, and can be identified even under LM by adjusting the microscopic focus. Other than this, it is not easy to find differences in the valve morphology. Neighboring species that are very similar in valve morphology to the two aforementioned species include C. subleptoceros Krammer and C. stigmaphora Østrup. Cymbella subleptoceros differs from C. neoleptoceros in that its valve width is narrower (7.5-10 vs. 8-12 μm) and the outline of the valve is much slender ( Krammer, 2002; Bahls, 2016b). Cymbella stigmaphora is characterized by a wide valve width of more than 10 μm and axial area is linear and very wide ( Krammer, 2002).

Occurrence. This variety was observed in several places in the Ian Stream in Sangju, South Korea, and also appeared in the Gapyeong section of the middle stream in the Bukhan River.

The variety and nominate variety, Cymbella neoleptoceros , are reported to be widespread, sometimes occurring in large numbers, in brooks and lakes in the mountains of the Alps and the Balkans ( Krammer, 2002). In the United States, the nominate was concentrated in two lakes near the northwest border ( Bahls, 2016b), and was recently discovered from Lake Tahoe ( Noble et al., 2023). Except for the two regions mentioned above, its distribution area is quite limited. Cymbella neoleptoceros has been reported from rivers along the Mediterranean coast of Italy, and Japan, and has also been found as a few fossils ( Ohtsuka et al., 2007; Tanaka et al., 2011; Falasco et al., 2016; Mutlu et al., 2022). However, the variety has only been reported from sediments in the Arctic region since Krammer’s designation as a new species. When looking at the reported cases, it seems that the variety and the nominate are not strictly distinguished taxonomically, but has been reported as C. neoleptoceros .