Tetralunata schoemanii, Kociolek, J. Patrick, Greenwood, Megan, Rogers, Dillan, Hamsher, Sarah E., Miller, Scott, Li, Jingchun, Chang, Aimee Caye G. & Taylor, Jonathan, 2024

Kociolek, J. Patrick, Greenwood, Megan, Rogers, Dillan, Hamsher, Sarah E., Miller, Scott, Li, Jingchun, Chang, Aimee Caye G. & Taylor, Jonathan, 2024, Light and Scanning Observations on a Denticula species reported from South Africa and endemism of the diatom genus Tetralunata (Rhopalodiales, Bacillariophyceae), Phytotaxa 652 (4), pp. 284-292 : 289-290

Tetralunata schoemanii , sp. nov.

Figures 1–21

Description: Valves are linear in shape with apices tapered and narrowly rounded. Length ranges from 23–55 µm and breadth 7–10 µm. The raphe is placed medianly, with the raphe branches indistinct. The proximal ends terminate close to one another. Distally, the raphe branches extend onto the mantle at the apices. Costae are robust, 1–3 / 10 µm. Striae are parallel, composed of 4–6 areolae, and number 8–10 / 10 µm. Areolae clover-shaped with 4–8 c-shaped occlusions with those closer to the raphe having more occlusions and complexity. In girdle view, “capitate costae” are visible. Also evident in girdle view are Häutung valves, with a single new valve produced within a frustule. Häutung valves appear arched or undulate but otherwise are structured similar to vegetative valves.

Type:— SOUTH AFRICA. Lesotho , about 2 miles from the Maluti treks camp, situated on the banks of the Senqunyane River, on the road to Marakabei. Sides of hollow, cave-like cliffs below the road, damp rock faces. (Holotype COLO! 652039, here illustrated as Fig. 3 ; isotypes BM! 82423, South African National Diatom Collection! 84/1673) .

Etymology:— Named in honor of F.R. Schoeman who collected and first reported this diatom.

The production of Häutung valves as initially reported was thought to be unique to the genus Epithemia ( Thaler 1972; Sims 1983), although Fricke (1906 in Schmidt) had illustrated it in Denticula vanheurckii (= T. vanheurckii (Brun) Hamsher et al. 2014: 361 ). Häutung valves were first described by Geitler (1927) and later in greater detail by Thaler (1972) as a single valve produced within a frustule that more or less resembles the vegetative valves, distinguishing it from Innenschalen (e.g. Geitler 1980; Kociolek et al. 2011) and valves produced within cells of Eunotia Ehrenberg (1837: 44) (e.g. Von Stosch & Fecher 1979). These valves may have undulate valve faces, making them distinct in the light microscope. The reason for their production is uncertain, but they may be reactions to osmostic stress or serve as a resting stage ( Thaler 1972).

Observations on the Tetralunata species from South Africa confirms their close relationship to Epithemia , as suggested by Hamsher et al. (2014). Evidence for a close relationship to Epithemia is evidenced with respect to the presence and similarity in structure in the volae, septa, septa that clasp the costate fibulae forming ‘capitate costae’, lack of a keel, no poroids in the girdle bands, frustules that are planar and not segment-like in their organization, and production of Häutung valves ( Sims 1983, Kociolek et al. submitted).

In terms of biogeography, Kociolek (2019) had indicated Tetralunata was endemic to Indonesia. Reporting the genus in South Africa here for the first time, as a species endemic to southern Africa, expands the known distribution of the genus considerably. Our current understanding is that the members of the Rhopalodiales have verified fossil records that extend back 30 mya ( Benson et al. 2012). Given the wide separation in both space and time of SE Asia and South Africa during the breakup of the continents ( McLoughlin 2001), earth history dynamics would not be useful to identify a mechanism for this disjunct distribution. Further research will be necessary to attain an understanding of the separate locations for this rare genus.

Figures

FIGURES 1–10. Tetralunata schoemanii, sp. nov. Light Microscopy. Figs 1–8. Size diminution series, valve views, from Holotype slide. Fig. 9. Septa. Fig. 10. Frustule in girdle view showing Häutung valve. Scale bar = 10 µm for all specimens.

FIGURES 11–15. Tetralunata schoemanii, sp. nov. Scanning electron microscopy. Valve exterior. Figures 11, 12. Valve view of entire cell. Scale bars = 5 µm. Figs 13, 14. Higher magnification view of volae occluding areolae, on valve face and mantle, respectively. Scale bars = 1.5 µm. Fig. 15. Girdle view showing the girdle bands near the valve apex. Scale bar = 2.5 µm.

FIGURES 16–19. Tetralunata schoemanii, sp. nov. Scanning electron microscopy. Internal views. Fig. 16. Valve view with costae evident. Scale bar = 10 µm. Fig. 17. Valve with septum overlaying valve. Scale bar = 5 µm. Fig. 18. Septum. Scale bar = 5 µm. Fig. 19. High magnification view of the center of the valve showing proximal raphe ends. Scale bar = 1 µm.

FIGURE 20, 21. Tetralunata schoemanii, sp. nov. Septum, cross section. Fig. 20. Septum only. Fig. 21. Valve with costa and septum overlaying the valve. Scale bars = 5 µm.