LM micrographs of Luticola tropica Levkov, Metzeltin & Pavlov in size diminution series (A–T) and isolated open copula U external view of valve (V, W) Detailed external views showing distal raphe ending X stigma opening Y proximal raphe endings with thread-like grooves (Y, Z) and areolae structure (X–Z). Internal view of valve AA detailed internal close-ups showing distal raphe ending AB proximal raphe endings and stigma opening AC. Scale bars: 10 µm (A–U), 5 µm (V, W, AA), 4 µm (X, Y, AB, AC), 3 µm (Z).