Edlund, M.,
Burge, D.
(2015).
Semiorbis.
In Diatoms of North America.
Retrieved May 01, 2026, from https://diatoms.org/genera/semiorbis?x-craft-preview=cab8b13ef68d1e257235fd2491770f51dfe0c9a6c0ad3b95411776e5316d603alxhbyabypv
Eunotioid
Semiorbis
Valves strongly lunate
Transapical, external costae
Spines on dorsal and ventral ends of costae
Valves are strongly lunate, with thick, external, transverse costae between striae. The costae often terminate in spines at the dorsal and ventral margins. A small, greatly reduced raphe is present at the poles. The raphe is typically not visible in LM. The proximal raphe ends are on the ventral margin, while the terminal fissures curve...