Orthoseira tropica (Krasske) Metzeltin & Lange-Bert. LM (A–E) and SEM (F–M) micrographs taken from sample 156 (Boisa Island, Papua New Guinea). A–E. LM pictures of valves in valve face view. F. Frustule in girdle view connected to each other with spines forming short chains. G–I. Frustule in girdle view showing the structure of the cingulum and linking spines. J. SEM external view of a valve in oblique view showing valve face structure. K. SEM external detail of central part of the valve face with carinoportulae. L. Internal view of a complete valve. M. SEM internal detail of the carinoportulae showing the slits between the carinoportulae, arranged in a star-shaped manner. Scale bars: A–J, L = 10 µm; K, M = 2 µm.