Synedra undosa from Grunow’s Honduras material A internal view of half valve, total length would have been ca. 690 µm B external view of fragment of frustule including the central inflation C external view of valve fragment with pole D external view of valve fragment near central area showing the strong undulation E detail of external pole showing annulus (double-headed arrow) and spines F–H internal views of central, near central (cf. D), and polar portions of valve, respectively, showing longitudinal costae (arrows) and transverse costae; transverse costae developing gradually toward left in H. I girdle bands, showing fimbriate valvocopula and copula with glimpses of interior costate surface of valve. Scale bars: 100 µm (A); 15 µm (B, C); 10 µm (D–I).