Achnanthidium atomus (Hustedt) Monnier, Lange-Bertalot & Ector, 2004

Lee, Sang Deuk, Yun, Suk Min, Cho, Pyo Yun, Yang, Hye-Won & Kim, Oe Jung, 2019, Newly Recorded Species of Diatoms in the Source of Han and Nakdong Rivers, South Korea, Phytotaxa 403 (3), pp. 143-170 : 152

Achnanthidium atomus (Hustedt) Monnier, Lange-Bertalot & Ector in Monnier et al. 2004 * Figures 6, 7

Original description: Monnier et al. (2004), p. 128, figs 1–41.

Key literature: Monnier et al. (2004), p. 128, figs 1–41.

Specimen examined: Tables 1, 2.

Dimension: Length 6.1–7.1 μm, width 2.7–2.9 μm; 26–28 striae in 10 μm on the raphe valve and 21–22 striae in 10 μm on the rapheless valve.

Description: The valves are slightly linear-elliptic with round ends. The raphe valve concave and rapheless valve convex along transapical axis. The striae are uniseriate, extending on the valve face. The foramen of the areolae small and circular on the valves. The raphe branches are filiform, simple slit in the middle part, small pin-hole at the central raphe ends, deflected in one direction in the proximal raphe endings. The striae are interrupted at the valve face and mantle junction by a weakly thickened hyaline area, parallel throughout the valve length, terminal short striae slightly radial. The areolae are small and round in valve view.

Remarks: A. atomus is closely related to A. atomoides from Java and Sumatra ( Indonesia) ( Monnier et al. 2004). It differs from commonly smaller valve sizes and by less spaced striae and areolae. A. atomus has 19–21 striae in 10 μm on the rapheless valve and 22–26 striae in 10 μm on the raphe valve, contrary to 22–28 and 25–32 striae in A. atomoides , respectively. A. atomoides has an average of 37 areolae in 10 μm in the rapheless valve and 45 striae in 10 μm in raphe valve, contrary to 50 areolae and 65 striae in A. atomoides , respectively ( Monnier et al. 2004).

Distribution and ecology: This species was found in two regions within Central and Northern Appalachia from Noth America (Ponader & Potapova 2007). It mainly distributed in nutrient-poor rivers within a narrow pH range from 8 to 8.3 (Ponader & Potapova 2007), but over a wide range of conductivity levels with a preference towards higher values (Ponader & Potapova 2007). The pH and nutrients were major factors driving the distribution of Achnanthidium atomus in Appalachia (Ponader & Potapova 2007).

Figures

FIGURES 2–7. LM (4) and SEM (2, 3, 5–7) microphotographs. 2–5. Achnanthes sinaensis. 6, 7. Achnanthidium atomus. (Scale bars: 2–5 = 10 μm; 6, 7 = 1 μm).