LM micrographs of Luticola halongiana Witkowski, M.Rybak, H-D.Nguyen & D-V.Nguyen sp. nov. in size diminution series (A–Z). Holotype specimen – black frame I external view of frustule (AA–AC). Internal view of frustule (AD). Detailed external close-ups showing distal raphe ending (AE), proximal raphe endings with small rounded grooves and opening of stigma (AF). Detailed internal close-up showing distal and proximal raphe endings, hymen structure and stigma opening (AG). Scale bars: 10 µm (A-Z), 5 µm (AA, AB, AC, AD), 3 µm (AE, AG), 1 µm (AF).