Eunotia, Ehrenberg, 1837

Furey, Paula C., Manoylov, Kalina M. & Lowe, Rex L., 2020, New and interesting aerial diatom assemblages from southwestern Iceland, Phytotaxa 428 (3), pp. 173-208 : 193-194

Eunotia

Eunotia species, considered all together, were common in our samples at relative abundances <5% ( Table 3), though at four sites the relative abundance reached 12–33% ( Table 2).

Eunotia arctica Hustedt (1937: 169) (LM = Fig. 4 G–I ; SEM = Fig. 4 M )

The valve morphology of E. arctica from these samples measured at length 23.4–25.7 μm, width inflated area 7.4–8.4, width middle 5.3–6.5 μm, 14.8–16.2 striae (middle) in 10 μm, 18.0–22.1 striae (ends) in 10 μm, and areolae ca 34 in 10 μm (for n=4 LM, n=1 SEM). The raphe curved strongly up the valve apex ( Fig. 4 M ).

This taxon only occurred at a few sites in Hengill and Þingvellir rift valley, but at <5% relative abundance ( Table 3). The checklist of algae from Iceland ( Hallgrímsson 2007) includes E. arctica . Lange-Bertalot et al. (2011) show images of specimens from Iceland (type locality), along with valves from Spitzbergen ( Svalbard) with a similar, but slightly different morphology (see outline of inflated areas; plate 73, figs 9–15).

Eunotia bidens Ehrenberg (1843b: 413) (LM = Fig. 5. K–L ; SEM = Fig. 5. G )

The valves observed measured at length 37.0–47.3 μm, width inflated area 11.0 – 12.3 μm, width middle 8.2–11.0 μm, 12.2–14.4 striae (middle) in 10 μm, and 12.2–17.0 striae (ends) in 10 μm (n = 3 LM, for n=3 SEM). The checklist of algae from Iceland includes E. praerupta var. bidens (Ehrenber 1843: 413) Grunow in Cleve & Grunow (1880: 109) ( Hallgrímsson 2007; considered a synonym of E. bidens ), and Petersen (1928a) briefly mentions this taxon. The valves in this study appear similar to a specimen shown in Foged (1974; E. praerupta var. bidens, Plate V. fig. 8). Our valves are too narrow and short to belong to E. superbidens Lange-Bertalot in Lange-Bertalot et al. (2011: 229).

Valves of E. bidens were only observed at <1% relative abundance in a bryophyte squeeze in the Þingvellir rift valley (WW 41; Table 2).

Eunotia bigibba Kützing (1849: 6) (LM = Fig. 5 A–F ; SEM = Fig. 5 H–I )

The valve morphology of E. bigibba measured at length 25–36.5 μm, width inflated area 9.8–11.4 μm, width middle 8.3–10.7 μm, 10.6–13.2 striae (middle) in 10 μm, 14.1–16.2 striae (ends) in 10 μm, and areolae 24–30 in 10 μm (for n=10 LM, n=7 SEM). The striae stopped short to give the appearance of the hyaline area (i) on the ventral edge of the valve ( Fig. 5 I ). In girdle view, the cingulum formed waves following the inflated areas of the dorsal margin ( Fig. 5 H ). The areolae extended across the valve mantle ( Fig. 5 H ).

The valves from Iceland align best with valve measurements for E. bigibba described from other populations in Lange-Bertalot et al. (2011; length 20–43 μm, width inflated area 8–14 μm, striae 10–12 in 10 μm, areolae ca. 30 in 10 μm). The shorter, narrower valves with higher striae density contrast with those of E. sarek Berg (1939: 449) (Length 40–57 μm, width inflated area 14–23 μm, striae 7–10 in 10 μm; Lange-Bertalot et al. 2011). The narrower depression between the inflated areas sets valves apart from those of E. suecica Cleve (1895: 29) .

Eunotia bigibba occurred in association with bryophytes and lichens in low densities (<5%) from a number of sites in the Hengill watershed, and at 12% on WW 41 in the Þingvellir rift valley ( Table 2). Eunotia bigibba , included in the checklist of algae from Iceland (as E. praerupta var. bigibba ( Kützing 1849: 6) Grunow in Van Heurck 1881; ( Hallgrímsson 2007), was also reported from epiphytic diatom assemblages from terrestrial mosses in in Zackenberg (Northeast Greenland; Van Kerckvoorde et al. 2000).

Eunotia curtagrunowii Nörpel-Schempp et Lange-Bertalot in Lange-Bertalot & Metzeltin

(1996: 48) (LM = Fig. 6 A–E ; SEM = Fig. 6 F–J )

The valve morphology of E. curtagrunowii measured at length 21–28 μm, width 7–8.5 μm, 9.4–13.0 striae (middle) in 10 μm, 14.4–18.0 striae (ends) in 10 μm, and areolae 30–35 in 10 μm (for n=10 LM, n=4 SEM). Valve measurements and morphological descriptions conform to those reported in Lange-Bertalot & Metzeltin (1996) and Lange-Bertalot et al. (2011). In our specimens, a single rimoportula occurred just below the midpoint of the valve apex with a simple, round opening externally ( Fig. 6 G ) and a raised opening internally ( Fig. 6 I ). Note the patterning, and single enlarged areola along the external, ventral margin ( Fig. 6 H ), also shown in other SEM micrographs ( Lange-Bertalot et al. 2011; plate 196, fig. 9–12, 13). The narrower valves distinguish specimens from Iceland from those of E. ewa Lange-Bertalot et Witkowski in Lange-Bertalot et al. (2011: 93) from Greenland (width 9.5–13 μm). The rectangular girdle view of valves from Iceland ( Fig. 6 D, E ) contrast with the parallelogram-like shape of the girdle view of a similar shaped taxon, E. parallelogramma Van de Vijver, M. de Haan et Lange-Bertalot (2014: 274) , reported from Antarctica.

Frustules occurred in association with bryophytes and lichen at 11% relative abundance at WW 1, and in low densities other sites in Hengill and the Þingvellir rift valley ( Table 2). Eunotia curtagrunowii is reported as E. praerupta var. muscicola Petersen (1928: 377) from terrestrial habitats in Iceland ( Petersen 1928 a, Broady 1978) and included in the checklist of algae from Iceland ( Hallgrímsson 2007).

Eunotia cf. neofallax Nörpel-Schempp et Lange-Bertalot in Lange-Bertalot et al. (1996: 3) (LM = Fig. 4 Q–W ) Valves observed measured at length 9.0–22.0 μm, width 1.7–2.5 μm, and 16–20 striae in 10 μm (for n=9 LM). Valves showed a similar outline to those of E. neofallax Nörpel-Schempp et Lange-Bertalot , though stria density in our specimens was slightly denser and the presences of a spine on the apex could not be confirmed.

Relative abundance occurred at>10% at one site in the Þingvellir rift valley and>20% at one site in Hengill ( Table 2). Previous reports of E. neofallax from intermittently wet subaerial habits included those with melting snow ( Bouchard et al. 2018).

Eunotia palatina Lange-Bertalot et Krüger in Werum & Lange-Bertalot (2004: 154) (LM = Fig. 4 A–F ; SEM = Fig. 4 J–L )

The valve morphology of E. palatina from our samples measured at length 24.2–38.5 μm, width middle 5.0–6.8 μm, 15–16 striae (middle) in 10 μm; 16–19 striae (ends) in 10 μm, and areolae 33–35 in 10 μm (for n=8 LM, n=2 SEM). Internal openings of the round areolae were not embedded in a groove ( Fig. 4 J ). A narrow hyaline area, from the short termination of the striae, extended across the ventral edge of the internal and external valve face, visible in LM (e.g. Fig. 4 B, D ) and SEM ( Fig. 4 J–i ). A slight internal thickening occurred on the internal ventral margin where the proximal raphe ended ( Fig. 4 J –ii).

Frustules occurred in association with bryophytes and lichen at low relative abundances (<5%) in Hengill and the Þingvellir rift valley ( Table 3). Lange-Bertalot et al. (2011) show specimens from a variety of aerophilous locations including the type population in Germany (see also Werum & Lange-Bertalot 2004, plate 7, figs 10–18) and the synonym from Iceland (as E. arctica var. simplex Hustedt 1937: 169 ), as well as Tara Mountains Poland, Southern Alps, Italy, Pyrenees, Andora.

Figures

FIGURE 4. Light (A–I, N–c) and SEM (J–M) images of aerial diatom assemblages from southwestern Iceland, Eunotia species. A–F, J–L. Eunotia palatina: A–F. size diminution series, the striae end short on the valve face to create the appearance of a hyaline strip (i), J. internal views of a valve apex showing the location of the helictoglossa, a hyaline area (i) and swelling where the proximal raphe ends (ii), K. a whole valve, internal view (scale bar as in L), and L. a frustule with both valve and girdle views visible; G–I, M. Eunotia arctica: G–I. valve views, M. external view shows striae and hyaline band along the ventral edge; N. Eunotia cf. valida: valve view; O–P. Eunotia cf. fallax: valve view; Q–W. Eunotia neofallax: valve view, V. half valve / half girdle view, and W. girdle view; X–c. Eunotia nymanniana: valve view. LM scale bar = 10 μm, SEM scale bars as shown.

FIGURE 5. Light (A–F, K–L) and SEM (G–I) microscopy images of aerial diatom assemblages from southwestern Iceland, Eunotia species.A–F, H–I. Eunotia bigibba:A. two live frustules in girdle view, C–F, I. valve view, B–F. size diminution series, and B. girdle view showing raphe position, H. arrangement of the cingulum and areolae on the mantle, and I. valve view showing arrangement of punctate striae and raphe ends on the valve face. Note the appearance of the hyaline area on the ventral edge of the valve where the striae stop short (i); G, K–L. Eunotia bidens: all valve views, note the swellings along the ventral margin where the proximal raphe ends. Frustule K slightly tilted. LM scale bar = 10 μm, SEM scale bars as shown.

FIGURE 6. Light (A–E) and SEM (F–J) microscopy images of aerial, diatom population of Eunotia curtagrunowii from southwestern Iceland. A–C. valve view size diminution series and D–E. girdle view with different focuses, F. internal view showing helictoglossa and internal opening of areolae with a close up of the apex of the same valve in I. to show the internal expression of the rimoportula (arrow), G. close up of valve apex with external opening to the rimoportula (arrow), H. external view, showing arrangement of striae and raphe ends on the valve face, note the markings along the ventral edge of the valve face, J. tilted girdle view showing cingulum. LM scale bar = 10 μm, SEM scale bars as shown.