Sellaphora mayrii M.L. García, Maidana, E. Morales & D.G. Mann, 2020

García, M. Luján, Morales, Eduardo A., Mann, David G. & Maidana, Nora I., 2020, Sellaphora mayrii (Bacillariophyceae), a new diatom from the Argentinean Patagonia, Phytotaxa 437 (3), pp. 135-146 : 138-141

Sellaphora mayrii M.L. García, Maidana, E. Morales & D.G. Mann sp. nov. (LM Figs 2–11 , SEM Figs 15–27 )

Description: —Valves elliptic-lanceolate with subrostrate and bluntly rounded apices ( Figs 2–11 , 15–20 ). The axial area is noticeably narrow and linear, slightly elevated from the valve face, featuring a very narrow conopeum ( Figs 15–17 ), which is possibly more developed in living cells. The central area is mainly rectangular to bow-tie shaped, bordered by striae formed by 1 to 3 (4) areolae on the margins, sometimes with alternation of short and long striae, not always symmetric at both sides of the valve. Raphe filiform. The external proximal endings are drop-shaped, slightly deflected to the primary side of the valve ( Figs 15–17 , 21, 25 ), and the internal ones are straight and not expanded ( Figs 18–20 , 26 ). The distal endings are long and strongly bent towards the secondary side externally ( Figs 15–17 , 22–23 ). Internally the slits end in a raised helictoglossa ( Figs 18–20 , 24 ), beyond which there is a larger foramen-like pit, occluded externally ( Fig. 24 ). Striae uniseriate, radiate, unresolvable in LM ( Figs 2–11 ). Areolae small, roundish, sometimes almost square ( Figs 24, 27 ). The areolae in internal views are occluded by dome-shaped hymens ( Figs 19 , 28 ). However, our sedimentary material was somewhat eroded and the areolae were mainly open holes ( Figs 24, 27 ). At the valve face-mantle junction, there is a marginal ridge ( Fig. 15 ). Polar bars indistinct.

Dimensions (n=35): length 11.0–21.5 µm, width 4.7–5.8 µm, striae 31–36 in 10 µm and areolae 40–50 in 10 µm.

Holotype: —Circled specimen in slide LPC 15860 ! England Finder M/33-2, represented here in Fig. 7 . Herbarium División Ficología “ Dr. Sebastián A. Guarrera ”, Museo de la Plata, Argentina.

Type locality: —Shallow-lake Laguna Gemelas Este (49°23’S, 72°54’W) Santa Cruz province, Argentina. Coll. Cecilia Laprida (2015).

Ecology: —The ecology of Sellaphora mayrii is difficult to estimate with certainty because it was found in Holocene samples in core GEM15–2, with a maximum abundance (circa 60%) between 26 and 29 cm depth (ca. 1900 AC) and with a scarce abundance in recent sediments (<10%). Sellaphora mayrii co-occurred with Encyonema silesiacum (Bleisch) D.G. Mann ( Round et al. 1990: 667) and Psammothidium marginulatum (Grunow) Bukhtiyarova & Round ( Bukhtiyarova & Round, 1996: 5). Nowadays Laguna Gemelas Este has an area of 0.04 km 2 and a maximum depth of 5. 2 m. At the moment of sampling, its surface water had electric conductivities of 16–20 µS· cm-1, pH values of 7.2–7.7 and temperatures of 3.2–7.9 °C. More characteristics about this shallow lake are described in Mayr et al. (2019).

Mayr et al. (2019) and García (2019) reported the new taxon as “ Sellaphora sp 1 ” in fossil sediments obtained from shallow-lake Laguna Verde (49° 12’S; 72° 58’W, Santa Cruz province, Argentina), between 10 and 20 cm depth in core VER17–1. In this case, the co-occurring species were another unkown Sellaphora and small fragilarioids. For the same lake but in surface sediment samples (with pH values of 8, temperature values of 6.2 °C and conductivity values of 18 µS· cm-1), Sellaphora mayrii was reported as Microcostatus sp. 1 by Echazú (2012, fig 13: 52–53, fig 41: 7) but the figures shown in her work, both in LM and SEM, show the new species we describe here. Echazú reports the assemblage to have been dominated by small fragilarioids and Tabellaria flocculosa (Roth) Kützing ( Kützing 1844: 127).

Etymology: —The new species is named after Dr. Christoph Mayr in recognition for his valuable research in paleolimnology in southern Patagonia.

Remarks: —The key features of Sellaphora according to Mann (1989) include the chloroplast morphology and some characteristics of sexual reproduction. Neither of these are known for S. mayrii since live material was not available. Nevertheless, S. mayrii has several other morphological features that, taken altogether, justify its inclusion in the genus Sellaphora as defined by Mann (1989) and subsequent authors (e.g. Round et al. 1990, Wetzel et al. 2015, Kulikovskiy et al. 2018). Some of these features are the elliptic-lanceolate valve outline; the protracted, subrostrate and bluntly rounded apices; wide raphe sternum; the proximal raphe endings deflected towards the primary side both externally and internally; the groove alongside the raphe externally; the uniseriate radiate striae (biseriate striae occur in a few species, Wetzel et al. 2015); the rectangular to “bow-tie” shaped central area; and the small round areolae, covered internally by circular to elliptical, domed hymenes. The larger foramen-like pit seen at the poles, which is occluded externally, has been observed in some other Sellaphora species ( Wetzel et al. 2015) and in Okhapkinia alexandrii Glushchenko, Kulikovskiy & Kociolek , a genus described within the Sellaphoraceae by Kulikovskiy et al. (2018:122); the function of the foramen is unknown. Our new taxon does have the apical pit but it is unclear if it is present or not in the similar species that we use to compare its morphological features since it has not been reported in the original descriptions, however it is present on the “ laevissima ” group.

Figures

FIGURE 2–11. Sellaphora mayrii sp. nov. Type material LPC 15860. Laguna Gemelas Este, Santa Cruz province,Argentina. LM images. Fig. 7 Illustrates the holotype specimen. FIGURE 12–14. Sellaphora smirnovii Chudaev & Gololobova, type material. Lake Glubokoe, Russia.

FIGURE 15–20. Sellaphora mayrii sp. nov. Type material LPC 15860. Laguna Gemelas Este, Santa Cruz province, Argentina. SEM images. FIGURE 15–17. External valve view.Notice the sharp edge of the longitudinal groove (arrow) and the marginal ridge (arrowhead) in Fig. 15. Fig. 16 presents white deposits of probable mineral origin on the valve face. FIGURE 18–20. Internal valve view. In Fig. 19, notice the dome-shaped hymenes internally occluding the areolae (arrow).

FIGURE 21–28. Sellaphora mayrii sp. nov. Type material LPC 15860. Laguna Gemelas Este, Santa Cruz province, Argentina. SEM images. FIGURE 21. Tilted external valve view. Notice the marginal ridge (arrow). FIGURE 22–23. Detail of the external apices view. FIGURE 24. Internal apex view. Notice the larger foramen-like (pit) (arrow). FIGURE 25. Detail of the external view of proximal raphe endings (drop-shaped). FIGURE 26. Detail of the internal view of the proximal raphe endings (straight). FIGURE 27–28. Close up of the internal view of the areolae, notice the dome-shaped hymens in Fig. 28.