Nitzschia vitrea Norman

GRAEFF, C. L., KOCIOLEK, J. P. & RUSHFORTH, S. R., 2013, New and Interesting Diatoms (Bacillariophyta) from Blue Lake Warm Springs, Tooele County, Utah, Phytotaxa 153 (1), pp. 1-38 : 28-30

Nitzschia vitrea Norman (1861: 7, pl. 2, fig. 4) ( Figs 138–154 )

Valves lanceolate, tapering to blunt asymmetrically-rounded apices. Length 42.0–195.0 µm, breadth 7.5–12.0 µm. Raphe eccentric with distinctly elevated keel. Fibulae distinct and variably spaced, with no central nodule evident ( Figs 140, 143 ). Fibulae number 4–6/ 10 µm. Striae distinctly punctate, and the striae may have some areolae missing giving the sense of longitudinal undulations in the striae ( Figs 138, 142 ). Striae number 23–27/ 10 µm. Areolae number within a stria is highly variable, due to the nature of the areolae, 10–30/ 10 µm. Striae appear to stop before the margin on the side opposite the keel where there is a longitudinal hyaline strip ( Figs 138–139, 142 ).

In the SEM the longitudinal hyaline strip opposite the keel is apparent ( Figs. 146, 148 ) and appears to be part of the valve mantle. There is an organized, nearly continuous row of areolae adjacent to the raphe ( Figs 148–150 ). The raphe is continuous at the valve center and much of the keel is unornamented ( Figs 145–150 ). Externally, the areolae are generally oval ( Figs 147–150 ) but they narrow on the inside of the valve ( Fig. 150 ) to become more elongate ( Figs 153–154 ). The striae are interrupted at the robust fibulae ( Figs 153–154 ) and then continue across roughly ⅔ of the valve mantle adjacent to the fibulae ( Fig. 152 ). Internally at the apex, a small helictoglossa is present.

Distribution:— Nitzschia vitrea was found rarely in samples from the main basin of Blue Lake and the surrounding marshes. It is most common in the marsh to the south of Blue Lake (COLO 8529).

Observations:—This species is part of the Lineares subgroup within the genus Nitzschia Hassall (Krammer & Lange-Bertalot 1988, Hustedt 1930). Mann (1980: figs 18–19) previously published two SEM images of this taxon, showing the steep mantle, many open cingula, and distinct keel, but otherwise SEM images of this species have not previously been published. The openings between the fibulae are quite narrow, making observations of the raphe around the middle of the valve difficult from the interior. The structure of the striae, apparent lack of areola occlusions, and the steep keel of this diatom make it quite distinctive among other members of the genus Nitzschia . The Lineares subgroup seems, from keys to the subgroups of the genus (e.g. Krammer & Lange-Bertalot 1988, Hustedt 1930), to have few distinguishing features. Further research will be necessary to understand if this is a natural group and to better place this subgroup within the Bacillariales .

Figures

FIGURES 138–144. LM. Nitzschia vitrea. Valve views showing the size diminution series. Scale bar: 10 µm.

FIGURES 145–150. SEM. Nitzschia vitrea. External views of six specimens. Fig. 145, View of the valve face with interrupted striae. Fig. 146, Girdle view of a valve showing the prominent keel and constriction at the valve center. Fig. 147, Valve view of the apex with the raphe positioned at the top of the keel. Fig. 148, Side view of the apex showing a complete row of areolae closest to the raphe and the hyaline region along the edge of the mantle. Fig. 149, Valve center with continuous raphe. Fig. 150, Broken valve showing the areola openings narrowing on inside of the valve. Scale bars: Figs 145–146: 20 µm; Figs 147–150: 1 µm.

FIGURES 151–154. SEM. Nitzschia vitrea. Internal valve views of three specimens. Fig. 151, Full valve showing variably spaced fibulae. Fig. 152, Tilted specimen showing striae that continue across roughly ⅔ of the valve mantle. Fig. 153, Apex with small helictoglossa and prominent fibula. Fig. 154, Central area showing elongate areolae and striae that are interrupted at the fibulae. Scale bars: Fig. 151: 20 µm; Fig. 152 µm: 10; Figs 153–154: 1 µm.