Placoneis modaomensis sp. nov. (Bacillariophyta; Cymbellaceae), a new species from Guangdong Province, China

One new species, Placoneis modaomensis, found in a freshwater environment from a tributary of the Pearl River, which lies in Modaomen Channel, Zhuhai County, Guangdong Province, China, is described based on light and scanning electron microscope observations. P. modaomensis sp. nov. has the morphological features that are typical for the genus, including external terminal raphe fissures curved to the opposite sides and areolae with internal volate occlusions. The new species is similar to P. amphibola (Cleve) E.J. Cox, P. amphiboliformis (Metzeltin, Lange-Bertalot & Soninkhishig) Vishnyakov, P. parvapolonica Lange-Bertalot & Wojtal, P. clementispronina Lange-Bertalot & Wojtal and P. nanoclementis Lange-Bertalot & Wojtal in the shape of the valves and in having coarse striae but it can be easily distinguished by the two main morphological characteristics: external central raphe endings bent in the opposite directions, and areolae covered by volate occlusions externally. The latter feature appears to be new for taxa assigned to the genus Placoneis. Data on the associated diatom flora and its ecology are also given. These findings increase our understanding about the morphology of Placoneis in general and the distribution of the genus in China.