Semiorbis eliasiae

Cells lunate with dorsal sides slightly broader compared to ventral sides, lanceolate in girdle view (Figs 29–36). Cells arranged in colonies constructed of four to many cells adjoined at their valve ends in circular groups with their dorsal mantles and cingula facing outward. Cells with a centrally located nucleus and two plate-like valve-appressed chloroplasts in each cell. Storage bodies common and likely polyphosphate (libroplasts) or chrysolaminarin (Figs 48–50). Valves lunate with somewhat broader dorsal mantles (Fig. 53), slightly rostrate ends, parallel margins that may be slightly constricted mid-valve in smaller specimens, and conspicuous external transapical costae (Figs 29–36). Valve length 16.5–40.5 µm, breadth 3.6–5.7 µm, stria or transapical costa density 8–12 per 10 µm, and dorsal curvature from 0.05 to 0.12. In scanning electron microscopy, transapical costae terminating dorsally and ventrally in short, flat spines at the facemantle junction. Costae continuing onto the valve mantle (Figs 51–53). A short raphe slit present at each valve end, externally starting on the ventral mantle and curving onto the valve face at each end (Fig. 52), internally limited to the ventral mantle and terminating in a small helictoglossa (Figs 54–55, 57). No rimoportulae present (Figs 55, 57). One stria between neighbouring costae (Fig. 53), striae uniseriate, sometimes becoming biseriate toward the face-mantle junction, and continuing onto the valve mantle (Figs 53, 56). Areolae without external occlusion, internally occluded by a hymen (Fig. 56). Cingulum of 3–4 split bands, each with a single row of areolae (Figs 52–53).

• Author
  Edlund, D.R.L.Burge, N.A.Andresen and VanderMeulen 2021
• Length Range
  16.5-40.5 µm
• Width
  3.6-5.7 µm
• Striae in 10µm
  8-12