Gomphonema insularum

Gomphonema insularum, sp nov. Figs 1–16, figure 1 is of the holotype

Valves linear with slightly convex margins. Footpole rounded in larger specimens, narrow in smaller specimens. Headpole rounded. Length 15.5–42.0 µm, breadth 4.5–7.0 µm. Striae not evidently punctate, radiate to slightly radiate from the center to the headpole, radiate to strongly radiate from the center to the footpole 9–13/10 µm. Raphe weakly undulate, proximal ends curve toward the single stigma. Axial area is broad and lanceolate, slightly tumid at midvalve, narrow at poles. Apical pore field (APF) distinct. Septa and pseudosepta present at poles.

In the SEM, striae appear composed of variously shaped areolae, including c-shaped, s-shaped, m-shaped, and apically-elongate slit-like areolae (Figs 9–11). Areolae closest to the axial area are primarily c-shaped. At the center of the valve, the axial area has a few shallow depressions, and transapically-elongate depressions appear at the internal end of most striae (Figs 9–11). Proximal raphe ends are dilated, and terminate close to one another (Figs 9, 11). Distal raphe ends are deflected away from the stigma-bearing side and extend onto the valve mantle (Figs 9, 10, 12). The raphe bisects an APF that extends onto the valve, the APF is composed of round porelli (Fig. 12). Internally, pseudosepta and helictoglossae are evident at the poles (Figs 13, 14, 16), with a flange evident on the footpole pseudoseptum (Fig. 16, compare with headpole in Fig. 14). Areolae are consistently shaped as seen through the foramina. Interstriae are robust, and a relatively wide axial area is visible (Fig. 13). Proximal raphe ends are strongly recurved, and have a flap that extends over the proximal curve (Figs 13, 15). On the slightly-raised central nodule, a transapically-elongate stigmal opening is present (Fig. 15).

Holotype: Holotype slide deposited in Bernice P. Bishop Museum, Honolulu (BISH 764122). Isotypes: JPK Collection 8304 at the University of Colorado (COLO) Type locality: Kauai, Waimea River at junction of Kukui and Waimea Canyon trails, coll.11 January, 2012. Etymology: Named for occurring on islands.

• Author
  Kociolek, Woodward and Graeff 2016
• Length Range
  15.2-42 µm
• Width
  4.5-7 µm
• Striae in 10µm
  9-13