Eunotia churiensis Veselá, Bohunická & Kaštovský, 2016

Kaštovský, Jan, Veselá, Jana, Bohunická, Markéta, Fučíková, Karolina, Štenclová, Lenka & Brewer-Carías, Charles, 2016, New and unusual species of cyanobacteria, diatoms and green algae, with a description of a new genus Ekerewekia gen. nov. (Chlorophyta) from the table mountain Churí-tepui, Chimantá Massif (Venezuela), Phytotaxa 247 (3), pp. 153-180 : 160-161

Eunotia churiensis Veselá, Bohunická & Kaštovský , sp. nov. ( Figs 5–8 )

Frustules rectangular in girdle view from the ventral side ( Figs 6G–J ), ca. 40–50 μm wide. Valves with moderately to strongly concave ventral margins and highly convex dorsal margins ( Figs 5A–L , 6A–F ), mostly with four wave crests on the dorsal margin (e. g., Figs 5A–E , 6A–C ), less commonly with three crests (in small valves, Figs 6D, F ) or transition between three and four crests, i. e., one of the crests close to the valve apex melting with the apex ( Figs 5G, J, L ). Valve crests bluntly pointed, the depressions between the crests wide and open ( Fig. 6A ). Valves relatively large for the genus, 54.5–115.5 μm long, 31.5–58.0 μm wide in the widest part of the valve, to 29–51 μm in between the crests and the center of ventral margin. Valve length-to-width ratio mostly around 2.1 (1.8–2.7). Valve apices variable from narrowly rounded (e. g., Fig. 6C ), truncated (e. g., Fig. 5E ) to round (e.g., Figs 5C , 6A ). Terminal nodules on the ventral side of the valve, not far from the apices ( Figs 5 , 6A–F ). Terminal raphe fissures curving onto the valve face, and pointing towards the dorsal part of the apex ( Figs 6A , 7B–D, F ). Helictoglossa is massive and well visible in LM ( Figs 5 , 6A–E ). Number and arrangement of rimoportulae variable, one to four (most commonly two) rimoportulae per each valve apex ( Figs 8C–E, H, I ), in total three to five per valve. Rimoportulae arranged individually ( Figs 8D, E ), as a group ( Fig. 8C ), or as a combination of both. External opening of each individual rimoportula (or a group of rimoportulae) mostly as an elongated pore ( Fig. 7B ), sometimes as a small round pore, located at the apex on the mantle ( Fig. 7D ) or on the junction of the valve face and mantle ( Fig. 7B ). Valves densely striated ( Figs 5 , 6A–F , 7A, C , 8A, F ), 14–17 striae in 10 μm near the center of ventral part of the valve, up to 22 striae in 10 μm at the wave crests due to the inserted striae ( Fig. 8B ), and 17–20 striae in 10 μm near the apices ( Figs 8E, H ). External small ridges in between striae irregularly spaced, giving the valve surface appearance of a “rough cloth” ( Figs 6A , 7A–H ). At the valve edges the small ridges fused in a certain extent, sometimes forming a web-like structure ( Figs 7G, H ). On the mantle, slightly below the valve edges, an elevated irregular siliceous rim-like structure present ( Figs 7B, C, E–G ). Externally areolae open, small and embedded in between the ridges ( Figs 7B, E, F, H ); internally areolae also unoccluded, well rounded and large ( Figs 8B, E, G ); 18–26 in 10 μm.

Type:— VENEZUELA. Bolívar State: Guyana Highlands, Chimantá Massif, Churí-tepui–Charles Brewer Cave Base Camp, Bathroom Creek, 5º 14.952’ N, 62º 1.588’ W, 2200 m a.s.l., J. Kaštovský 107, 20 January 2012 (holotype: ANSP!, slide GC 26823, specimen 12.0 mm south by 23.3 mm east from the benchmark cross on the slide, here illustrated as Fig. 6A . Isotype: CBFS!, slide A-053, specimen 6.7 mm south by 18.8 mm east from the benchmark cross on the slide, here illustrated as Fig. 5I ).

Etymology:—From the Latin adjective churiensis (from the table mountain Churí-tepui), referring to the area where the species was discovered.

Ecology and distribution:—This taxon occurred only at a single site, i. e., Bathroom Creek near the Charles Brewer Cave Base Camp as an epiphyte on an unidentified red alga (Rhodophyta).

Comparison with similar taxa:—Without any doubt, the morphologically most similar taxon to E. churiensis is the here described E. multirimoportulata . They both share very similar valve outline and dimensions (valve length, width, striae and areolae density). Main features separating these two taxa are different number of rimoportulae, length-to-width ratios and striae density at apices (all higher in E. multirimoportulata , Table 4), softer arching of the valve crests in E. multirimoportulata (correlating with a smaller crest height, Fig. 10A , Table 4B), and their different ecology (inhabiting a creek vs. a pool, although both growing epiphytically on red algae).

Eunotia churiensis is very similar in its valve outline to Eunotia tetraodon Ehrenberg (1838: 192) , having valves with moderately concave ventral margins and highly convex dorsal margins, and with four wave crest in most cases. However, Eunotia c huriensis possesses valves approximately two times larger as opposed to 22–70 μm long and 10– 24 μm wide valves of E. tetraodon ( Lange-Bertalot et al. 2011, Table 4A). Furthermore, valves of E. churiensis have a slightly denser striation compared to E. tetraodon (Table 4A). Unfortunately, Lange-Bertalot et al. (2011) and other authors did not provide any information about the presence of rimoportulae in E. tetraodon . A single picture known to us, i. e., plate 105, fig. 1 in Lange-Bertalot et al. (2011), indicates that this taxon might possess up to two rimoportulae at one apex and none on the other apex, unlike E. churiensis with at least three rimoportulae present on each valve. Additionally, the valve face of E. tetraodon is smooth (plate 103, fig. 3, 4, Lange-Bertalot et al. 2011) without any hint of ridges as observed in valves of E. churiensis .

Eunotia semicircularis ( Ehrenberg 1854: pl. 16, fig. 31a) Lange-Bertalot & Metzeltin in Lange-Bertalot et al. (2011: 216) also bears resemblance in the valve outline to E. churiensis , although can be easily distinguished based on its small size, lack of rimoportulae and geographic distribution (Scandinavia and the Arctic, Table 4B).

Small valves of E. churiensis could be potentially mistaken for E. triodon Ehrenberg (1837: 45) . However, valves of E. triodon have much smaller width, do not possess any rimoportulae and do not occur outside of Holarctic region (Table 4).

Figures

FIGURE 5. Eunotia churiensis, sp. nov. Size diminution series and the variation of the valve shapes of the population from the type locality in LM (part 1). Fig. 5I represents the isotype specimen. Scale bar = 10 μm.

FIGURE 6. Eunotia churiensis, sp. nov. Size diminution series and the variation of the valve shapes of the population from the type locality in LM (part 2), including girdle views. Fig. 6A represents the holotype specimen with well visible multiple rimoportulae on both apices (white arrows). White lines draw attention to the typical different shape of the top of the crests versus the area in between the crests (compare to Fig. 10A). “=” indicate the same specimen in different foci. Scale bars = 10 μm.

FIGURE 7. Eunotia churiensis, sp. nov., external views in SEM. Valve overviews (A, C), details of the uneven valve surface (E, H) and the mantle (E), close-ups of the apices (B, F) with an opening to rimoportula on the tip (B, white arrow), detail of the external raphe ending and rimoportulae (white arrows) on the valve mantle together with a valvocopula (D), and the arrangement of the girdle bands (G). “=” indicate different parts or views of the same specimen. Scale bars = 10 μm (A, C, G) or 1 μm (B, D–F, H).

FIGURE 8. Eunotia churiensis, sp. nov., internal views in SEM.Valve overviews (A, F), detail of the arrangement of striae changing from the ventral towards the dorsal part of the valve (B), close-ups of apices (C–E, H, I) with a various number and layout of rimoportulae (3 in C, D; 2 in E, H, I), and a detail of internal openings of areolae (G). “=” indicate different parts or views of the same specimen. Scale bars = 10 μm (A, E, F) or 1 μm (B, C, D, G–I).

FIGURE 10. Eunotia multirimoportulata, sp. nov. Size diminution series and the variation of the valve shapes of the population from the type locality in LM (part 2). Thick white lines in Fig. 10A draw attention to the typical similar shape of the top of the crests and the area in between the crests (compare to Fig. 6A). The thin white lines in Fig. 10A illustrate the method used for measuring crest heights (a distance from a line drawn between the centers of two surroundings saddle parts to the top of the crest). “=” indicate the same specimen in different foci. Well visible multiple rimoportulae are marked with white arrows. Scale bars = 10 μm.