Abstract: A nanodiatom genus, Fragilariopsis Hustedt, is newly recorded in China. This genus is characterized by, (1) cells in ribbons united by the entire or the greater part of the valve surface, (2) raphe strongly eccentric, (3) approximately equal numbers of interstriae and fibule, (4) apical axis often heteropolar, and (5) striae with two rows of poroids, seldom one or more than two. A detailed description of the taxonomic characteristics of the genus is given. The two species distributed in East China Sea and Huanghai Sea of China, F. kerguelensis (O’Meara) Hustedt and F. rhombica (O’Meara) Hustedt, were observed under TEM and photographed.

Key words: East China Sea, Huanghai Sea, nanodiatom, Fragilariopsis