Cavinula hilliardii Manguin ex Kociolek & Reviers

Cvetkoska, Aleksandra, Levkov, Zlatko, Hamilton, Paul B. & Potapova, Marina, 2014, The biogeographic distribution of Cavinula (Bacillariophyceae) in North America with the descriptions of two new species, Phytotaxa 184 (4), pp. 181-207 : 187

Cavinula hilliardii Manguin ex Kociolek & Reviers ( Figs 112–122 )

Basionym: Navicula hilliardii Manguin ex Kociolek & Reviers 1996

Valves linear to linear-elliptic with broadly rounded apices. Valve length 16–26 µm, width 8–10 µm. Striae punctate, parallel to weakly radiate at the apices, 18–24 in 10 µm. Striae sometimes curved towards apices. Areolae round, easily visible in LM, 25–30 in 10 um. Axial area narrow linear, central area absent to weakly defined. Raphe broad, slightly curved towards proximal raphe fissures; proximal fissures weakly expanded, distal fissures deflect to opposite sides of the valve.

Type: –– Lake Karluk , Alaska. Manguin 1960, fig. 2: 7 (holotype line drawing)

Observations:— Cavinula hilliardii is a rare species presently confirmed from LM images. The valves are linear to linear-elliptical, and the lower density of areolae is distinctive for this taxon. In LM, the raphe is broad, easily visible and has some similarity to C. jaernefeltii . The lower areola density and the curved terminal raphe fissures separate this taxon from C. jaernefeltii .

Distribution:— Currently identified from the Arctic, Alaska, Axel Heiberg Island in the Arctic Archipelago. Based on the observations of Foged (1981) and this study, C. hilliardii has a more restricted northern distribution in oligotrophic and alkaline habitats across the Arctic and Alaska.

Distribution Records:— Manguin (1960, fig. 2: 7, line drawing, Alaska), Foged (1981, fig. 30: 9–11, Alaska).

Figures

FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. Figs 107–111. Cavinula scutiformis (Grunow ex A. Schmidt) Mann & Stickle. Figs 112–122. Cavinula hilliardii Manguin ex Kociolek & Reviers. Figs 123,124. Cavinula variostriata (Krasske) Mann in Round, Crawford & Mann. Figs 125, 126. Cavinula lapidosa (Krasske) Mann. Figs 127–131. Cavinula pusio (Cleve) H. Lange-Bertalot in Werum & Lange-Bertalot. Figs 103, 104. W. Smith, Omersby, 1853 (type slide). Figs 126, 128. BRM N14/87a (Krasske material near Hessen). Scale bar: 10 µm.