Marine and brackish D.G.Mann (Bacillariophyta) species from the Java Sea and South China Sea coasts with the description of three new species.

In this study, samples were collected from the Java Sea coasts, from the South China Sea in Hainan Island coasts and Quảng Yên region and Rú Chá mangrove near Hue in Central Vietnam. In studied samples a total of eight species have been observed. Three of the taxa studied are described herein as species new to science - , and Under light microscopy (LM) and are similar with rhombic-lanceolate to rhombic/ elliptic-lanceolate to elliptic valve shapes and narrowly rounded apices. Both species can be easily distinguished by stria density (higher density in ). Under SEM is characterized by cribrate areola occlusions, a character thus far observed only in three established species. The remaining species of the whole genus known thus far are characterized by hymenate areola. Similar morphology species have been observed from tropical mangrove forests from Madagascar but they all can be easily distinguished based on the lack of grooves in the central area. The third species - has rhombic-elliptic to rhombic-lanceolate valves with broadly rounded to slightly protracted apices in larger specimens. This species has a relatively broad central area. Also unique among brackish-water is the small, rounded stigma positioned almost midway between the valve center and valve margin. In the habitats from which the new species are described we also identified five established taxa including, , , , and . For those species we provide detailed SEM characteristics of valve ultrastructure, as well as the range of environmental conditions and geographic distribution within the study area.