Eunotia giraffensis 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 : 23-24

Eunotia giraffensis Siver, Oddsund & Lott sp. nov. (LM Figs 1–8 , SEM Figs 9–14 )

Description:— Valves are slightly dorsi-ventral, elongate, with broadly rounded and obliquely rostrate apices that are deflected slightly towards the dorsal margin ( Figs 1–8 ). Valves range in length from 26–68 µm with a mean of 39 µm, and in diameter from 3.2–6.5 µm with a mean of 3.7 µm (n = 40). The ventral margin is slightly concave, becoming almost linear on smaller valves, and is more or less parallel with the dorsal margin, and of equal diameter throughout except at the apices. Small spines may be present on the virgae between the striae on the valve margin. Striae range from 16–25 per 10 µm, with a mean of 22. Striae are evenly spaced, parallel over most of the valve, becoming more closely spaced towards the apices ( Figs 1–8 ). Striae are continuous from the valve face onto the mantle on both the ventral and dorsal sides ( Figs 10, 12–14 ). Areolae are small, circular, closely spaced, and open on both the external and internal valve surfaces. The mantle is deep, approximately 3.5–4 µm, and forms a right angle with the valve margin on both the ventral and dorsal sides ( Figs 11–14 ). The margin of the mantle is thickened around each apex ( Figs 10, 12 ). The proximal end of the raphe commences midway down the mantle ( Figs 13–14 ). From this point, the raphe rises slowly until it reaches the valve margin, then turns approximately 45º up onto the valve face, terminating midway across the valve face close to the apex. The portion of raphe on the valve face is straight and the distal end is not curved or recurved ( Figs 9, 11 ). A distinct hyaline zone extends approximately 3 µm from the proximal end of the raphe towards the center of the valve ( Figs 13–14 ), is continuous along the lower side of the raphe, and extends up onto the valve face terminating near the apex. The striae are more closely spaced on the mantle below the raphe ( Figs 13–14 ), and a discontinuity zone is often observed midway along the raphe. Internally, the distal raphe fissure terminates within a thick and well-formed helictoglossa ( Figs 10, 12 ), which in turn is surrounded by a hyaline zone. A single rimoportula is found at one of the valve apices ( Fig. 12 ).

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 B” Canadian Museum of Nature CANA 129307 = Fig. 7 . Isotype circled specimen on slide “ GP 16-3 - 42 C” P. Siver’s personal collection = Fig. 5 ) .

Etymology:— The species epithet refers to the type locality.

Figures

FIGURES 1–8. LM micrographs of Eunotia giraffensis sp. nov. from the Giraffe Pipe fossil locality. Figure 5 is the isotype specimen circled on slide “GP 16-3-42 C” in P. Siver’s collection. Figure 7 corresponds to the type specimen circled on slide “GP 16-3-42 B” (CANA 129307). Scale bar = 10 µm.

FIGURES 9–14. SEM micrographs of Eunotia giraffensis sp. nov. from the Giraffe Pipe fossil locality. 9, 11. Close-ups of the end of a valve face showing the straight distal raphe end and the closer-spaced striae at the valve apex. 10, 12. Internal views of the helictoglossa and distal raphe end. Note the extended hyaline region surrounding the helictoglossa, thickened margin of the valve around the apex, densely-spaced striae on the mantle below the raphe, and the presence of a rimoportula. 13, 14. Girdle views of the ventral mantle depicting the position of the raphe, hyaline region surrounding the raphe, and the densely-spaced striae on the mantle below the raphe. Scale bars = 2 µm (Figs 9–12, 14), 3 µm (Fig. 13).