Eunotia pseudonaegelii Siver, Oddsund & Lott, 2022

Siver, Peter A., Oddsund, Erik & Lott, Anne M., 2022, Descriptions of three new diatom species in the genus Eunotia (Eunotiaceae, Bacillariophyta) from the Eocene Arctic, Phytotaxa 567 (1), pp. 21-35 : 26-28

Eunotia pseudonaegelii Siver, Oddsund & Lott sp. nov. (LM Figs 28–35 , SEM Figs 36–41 )

Description:— Valves are long and narrow, linear to slightly lunate, and with slightly protracted apices ( Figs 28–35 ). Valves range in length from 44–91 µm with a mean of 64, and in diameter from 2.4–4.3 µm with a mean of 3.4 (n=30). The ventral and dorsal margins are more or less parallel resulting in a similar diameter over most of the valve. Small spines are present on the virgae along both valve margins, and often around the apices ( Figs 36–38, 40–41 ). Striae are evenly spaced, parallel, continue from the valve face onto the mantle, range in density from 17–20 per 10 µm and a mean of 19. Areolae are small, circular, closely spaced, and open on both the external and internal valve surfaces ( Fig. 36–41 ). The mantle is shallow, often not more than 1 µm in depth, and forms a right angle with the valve margin on both the ventral and dorsal sides ( Figs 38–39, 41 ). The raphe is approximately 6.5–8 µm long. The proximal end of the raphe is positioned near the bottom of the ventral mantle, rises on a more or less 45º linear path, curves up onto the valve face, and with the distal end terminating in a small pore about 1/3 the distance across the valve face ( Figs 36, 38, 40 ). Internally, the raphe is slightly elevated from the mantle, especially near the proximal end, and the distal end terminates within a small, well-formed, helicoglossa ( Figs 37, 39 ). The striae below the raphe are typically reduced to a single row of pores ( Figs 37, 39 ). Internally, the distal raphe fissure terminates within a thick and well-formed helictoglossa, which in turn is surrounded by a hyaline zone ( Figs 37, 39 ). A single rimoportula is found per valve ( Figs 37, 39 ).

Type:— CANADA. Lac de Gras kimberlite field region, Northwest Territories: Rock specimen sub sampled from section 16-3-42 of the Giraffe Pipe core (holotype circled specimen on slide “ GP 16-3 - 42 E” Canadian Museum of Nature CANA 129309 = Fig. 31 ) .

Etymology:— The name refers to the similarity in shape with Eunotia naegelii , but reflects the fact they are not the same organism.

Co-occurring organisms:— The extensive portion of the core harboring all three of the new Eunotia species contained other species of Eunotia , species of the closely related genus, Actinella , and extensive concentrations of chrysophyte microfossils. In addition to numerous and many types of chrysophyte cysts, remains of three synurophytes, Mallomonas lychenensis Conrad (1938: 1) , M. porifera Siver & Wolfe (2005b: 300) and Synura cronbergiae Siver (2013: 181) were also dominant throughout this section of the core. Remains of euglyphid testate amoebae and sponge spicules were consistently present as well, but in smaller numbers relative to lower sections representing earlier time periods in the history of the lake.

Figures

FIGURES 28–35. LM micrographs of Eunotia pseudonaegelii sp. nov. from the Giraffe Pipe fossil locality. Figure 31 corresponds to the type specimen circled on slide “GP 16-3-42E” (CANA 129309). Scale bar = 10 µm.

FIGURES 36–41. SEM micrographs of Eunotia pseudonaegelii sp. nov. from the Giraffe Pipe fossil locality. 36, 38, 40. Exterior views of the end of a valve showing the position of the distal raphe end that extends only a short distance onto the valve face. Note the small spines along the dorsal margin and apex. 37, 39. Internal views of the distal raphe end, helictoglossa and position of the well-developed rimoportula. Note the shallow depth of the mantle. 41. Internal view depicting continuation of the striae on the valve face onto both the ventral mantle and the dorsal mantle. Note the spines along the dorsal valve margin. Scale bars = 2 µm (Figs 36–39, 41), 3 µm (Fig. 40).