Gomphoneis tumida (Tuji, 2005)

Kociolek, John P., Kulikovskiy, Maxim S. & Solak, Cüneyt N., 2013, The diatom genus Gomphoneis Cleve (Bacillariophyceae) from Lake Baikal, Russia, Phytotaxa 154 (1), pp. 1-37 : 10-11

Gomphoneis tumida (Skvortzow in Skvortzow & Meyer) Kociolek & Stoermer (1988: 104)( Figs 89–119 , 382–387 )

Valves lanceolate clavate, with broadly rounded headpole and rounded footpole. Axial area narrow, expanded to form an orbicular central area containing 4–6 isolated stigmoids. Length 25–51 µm, breadth 6-9 µm. Raphe lateral, with proximal ends just reaching into the central area. Striae costate, radiate about the center, becoming parallel towards the apices. Striae 14-19/ 10 µm. Apical pore fields distinct. Septa and pseudosepta present at the apices.

Externally in the SEM G. tumida has proximal raphe ends that are dilated, and 4 isolated stigmoids with rounded openings ( Fig. 382 ). Internally, the central area is rounded, and bears the internally raised central nodule ( Figs 383–387 ). The proximal raphe ends are received in the same direction. The stigmoidal openings are elliptical in outline and have teeth-like projections ( Figs 383–387 ). Helictoglossae are positioned at the poles. There are both septa ( Fig. 383 ) and pseudosepta ( Figs 385, 386 ) at the poles.

Observations:— This represents a more narrow view of this taxon than the one presented by Kociolek & Stoermer (1988b), but it is still considered one of, if not the most variable species present in Lake Baikal. This species is more linear than G. tumidioides .

Figures

PLATE 5: LM. Figs 89–119: Gomphoneis tumida. Scale bar = 10 µm for all figures.

PLATE 13: SEM. Gomphoneis tumida. Figs 382–387: Fig. 382: External valve view. Arcuate raphe has dilated proximal ends and deflects onto the mantle at the poles. Striae are composed of round areolae in two rows. Figs 383–387: Internal valve views. Fig. 383: Full valve view showing rounded central area and prominent pseudosepta at the poles. Fig 385: Specimen without girdle bands shows septa at the poles and the large helictoglossae. Fig. 386: View of valve from central area to footpole, showing narrow axial area, and robust striae and interstriae. Septum is evident at footpole. Fig. 384: Central area showing the proximal raphe ends recurved in the same direction and rounded to ellipsoidal stigma openings occluded by teeth-like projections. Fig. 387: Central area showing the inwardly raised central nodule, with the stigmoids in depressions around the base and the elevated raphe ends recurved at its margin. G. sublanceolata. Fig. 388: External valve view shows the dilated proximal raphe ends, simple, rounded stigmoidal openings and striae composed of rounded, unoccluded areolae. The striae terminate with a single areola along the length of the valve.