Placoneis sinensis Li & Metzeltin, 2013

Gong, Zhijun, Li, Yanling, Metzeltin, Ditmar & Lange-Bertalot, Horst, 2013, New species of Cymbella and Placoneis (Bacillariophyta) from late Pleistocene Fossil, China, Phytotaxa 150 (1), pp. 29-40 : 35-37

Placoneis sinensis Li & Metzeltin sp. nov.

Plate 6 , Figures 40–43; holotype specimens is represented in plate 5, figure 40.

Description: Valves broadly elliptical with slightly protracted, bluntly rounded ends. Length 44–78 µm, breadth 21–27 µm. Axial area weakly linear-lanceolate. Central area large, elliptic-rhombic, or irregularlyshaped, because of irregularly alternating shorter and longer striae. Raphe filiform, central ends appearing expanded with comparatively widely spaced central pores. Terminal fissures subapically deflected to opposite sides, but finally curved to the same side. Striae radiate throughout, 7–11/ 10 µm, composed of a single row of densely spaced areolae about 17–19/ 10 µm. Raphe fissures almost are straight with central ends faintly expanded, and scarcely discernible gently inclined to the secondary side (Figure 43).

Holotype: JH 91010-3, Museum of Nanjing Institute of Geography and Limnology, CAS, Nanjing, China

Type locality: Jianghan Palin , Hubei Provice. 30 o 11 ’ 18”N, 112 o 35 ’ 33”E .

Etymology: The Latin name sinensis refers to China.

Differential diagnosis: Distinguished from all species of the P. juriljii Miho & Lange-Bertalot (2006:27) by size of valve and lacking stigmata near the central nodule. Miho and Lange-Bertalot (2006) described P. juriljii with 2 stigmata near the central nodule and distinctly separated from the striae unilaterally, one or some additional stigma-like areolae occur closer to, but somewhat isolated from, the striae, 40–73µm in length, 16– 20 µm in breadth.

Many more specimens also have been found in the Namsan and Malikha rivers, both in the north of Myanmar, near the city of Putao. Malikha is one of two source-rivers of the biggest Myanmar-river, the Ayeyarwady. Specimens are shown in plate 7 (Figs. 44–49).

Placoneis sinensis is similar to Navicula obtuseprotracta Hustedt (1966:767) . This is a Placoneis species , found only as a fossil in the Columbia River, Oregon, U.S.A. and remarkably similar but not the same. The data from Hustedt are: length 60–72 µm, breadth 20–30 µm; striae 9–10/ 10 µm, near the poles c. 12, puncta 10–12/ 10 µm, near the axial area more dense about 16 in 10 µm.

Length, breadth and stria of P. sinensis and N. obtuseprotracta are very similar, only the densities of areolae are different. Our specimens differ the Hustedt’s taxon by broader apices. See my plate with photos of N. obtuseprotracta have been taken by Simonsen (1987).

Given the comparison of our new Placoneis to the Navicula species of Hustedt, we propose here a new combination from Navicula to Placoneis :

Figures

PLATE 6, Figures 40–43: Placoneis sinensis Li & Metzeltin sp. nov. Light microscopy images showing the range of variation within the type population. Figure 40. SEM, external valve.