Sellaphora tanghongquii sp. nov. (Bacillariophyta, Sellaphoraceae), a new diatom species from the Southern China

Sellaphora tanghongquii sp. nov. is described from epilithic samples taken from river systems in Southern China. The morphology of the new species is described based on light microscopy (LM) and scanning electron microscopy (SEM), and detailed ecological information is provided. This species has diagnostic features consistent with the genus Sellaphora, including small and linear valves, undulate and filiform raphe, and the presence of internal hymenate occlusions. Compared to morphologically similar species, we found that the new species is the most similar to S. constrictum in valve size and outline, raphe structure, and the external arrangement of the striae. However, S. tanghongquii sp. nov. has the following outstanding features which distinguish from similar species: 1) the valve striae are uniseriate externally and biseriate internally, 2) the shape of areolae are mostly square to elliptical, partly round, oval or irregularly shaped, composed of 2-4 small holes inside externally and round, elliptical, C-shaped, or irregularly shaped internally, 3) undulate valves with a slight constriction near the central portion of the valve, and 4) the presence of a row of separated and small pores on the valve mantle. The species appears to be best assigned to the group of species with axial grooves, which includes the generitype of Sellaphora. The discovery of this new diatom species increases the known biodiversity of the southern regions in China.