Gomphonema chemeron Jeff.R.Stone, Westover & Kociolek, 2020

Stone, Jeffery R., Kociolek, J. Patrick & Westover, Karlyn S., 2020, Two multi-stigmate Gomphonema species of Africa: Gomphonema kalahariense (nom. nov., stat. nov.) and Gomphonema chemeron (sp. nov.), Phytotaxa 436 (3), pp. 270-282 : 276-279

Gomphonema chemeron Jeff.R.Stone, Westover & Kociolek sp. nov. Figures 20–33

Description: Frustules in girdle view wedge-shaped with rows of coarser areolae on the mantle separated from the transapical striae by a structureless zone. Valves weakly clavate, rhomboid-lanceolate, with broadly-rounded apices. Length 38–88 µm, width 10–16 µm. Axial area wide, with a unilaterally-expanded central area due to the presence of shortened stria. Raphe lateral. Transapical striae uniseriate, distinctly radiate, 7–9 in 10 µm, but at the poles slightly denser (10 in 10 µm). Stigmata (3)4–7 present in the central area, with the number present positively related to valve length. At the border of the central area, striae on the side opposite of the stigmata often end with slightly detached, stigmoid areoles. Footpole with a bilobed apical pore field. Septa and pseudosepta are present at both poles.

In the SEM: Striae have roughly 22 (20–24) areolae in 10 µm that are coarsely punctate and uniseriate. Stigmata are expressed internally as slits and externally are simple openings. Internally, the proximal raphe ends hook sharply toward the stigmata. Proximal raphe ends lack distinctive central pores. The distal raphe ends terminate internally as small, distinct helictoglossae.

Holotype: Circled specimen on slide 585030 in the JPK Collection at the University of Colorado ( COLO)( Fig. 21 ).

Isotype: Circled specimen on slide 585031 in the JPK Collection at the University of Colorado ( COLO).

Type Locality: Baringo Basin (0.55458°N, 35.93748°E), Kenya.

Note: The species name is representative of the geological formation ( Chemeron Formation ) in which the diatom has been observed. To date, G. chemeron has only been observed in diatomite deposits of the Baringo Basin, Kenya approximately 2.6 million years of age.

Differential diagnosis: G. chemeron can be distinguished from G. kalahariense by the population size range, length:width ratio, and the range of number of stigmata present (see Table 1, Figs. 18 , 19 ).

Figures

FIGURE 18. Measurements comparing populations of multi-stigmate Gomphonema from Baringo and Kalahari populations. A) Valve length vs. valve width. B) Valve length vs. number of stigmata.

FIGURE 19. Biplot data from 25-point landmark analysis showing morphologically-distinct populations of Gomphonema species at Baringo Basin and Kalahari Basin sites.

FIGURES 20–27. Light microscope images of Gomphonema chemeron. Scale bar = 10 µm.

FIGURES 28–33. SEM images of Gomphonema chemeron. Figs. 28, 29. External views. Fig. 28. Girdle view at the apex with uniseriate rows of areolae comprising striae evident. Fig. 29. Valve view of central area with numerous (4) stigmata present. Figs 30-33. Internal views. Fig. 30. Entire valve view. Central nodule has 5 stigmata openings and recurved proximal raphe ends. Fig. 31. Central area to headpole, with central nodule bearing 3 stigmata openings and recurved proximal raphe ends. At the headpole, both a septum and pseudoseptum are present. Fig. 32. Footpole with prominent pseudoseptum evident, covering the helictoglossa. Fig. 33. Entire valve, with central nodule bearing 4 stigmata openings and proximal raphe ends barely visible. Striae can be seen extending onto the mantle. A remnant pseudoseptum is present at the headpole. Scale bars are indicated in the images.