(Hohn and Hellerman) Lange-Bertalot and Metzeltin 1996 Category: Symmetrical biraphid
BASIONYM: Navicula americana var. alastos Hohn and Hellerman 1963
Contributor: Loren Bahls -
Length Range: 41.0-82.0 µm
Width Range: 11.0-17.0 µm
Striae in 10 µm: 17-19 midway between valve center and apex
Valves are broadly linear, with parallel or weakly concave margins. Apices are obtusely rounded. The axial area is narrow and undulate, bordered on each side by a narrow conopeum. The conopea are continuous through the central area, where they expand laterally. Near the valve apex, the conopea are somewhat inflated before they terminate in a point. The central area is wide and transversely rectangular. The central nodule, defined by the inner margins of the conopea, is small, elliptic, and somewhat asymmetric. The raphe is filiform and follows the undulate margins of adjacent conopea. Proximal raphe ends are deflected slightly to one side and tipped with small pores. Distal raphe ends are comma-shaped. Striae surrounding the central area are parallel, straight, shorter, and more widely spaced than more distal striae, which are curved and radiate.
Basionym: Navicula americana var. alastos
Author: Hohn and Hellerman 1963
Length Range: 56.7 µm
Width Range: 12.5 µm
Striae in 10 µm: 12 at valve center, 16 near the apices
Hohn, M.H. and Hellerman, J. (1963). The taxonomy and structure of diatom populations from three Eastern North American rivers using three sampling methods. Transactions of the American Microscopical Society 82(3):250-329.
Lange-Bertalot, H. and Metzeltin, D. (1996). Indicators of oligotrophy - 800 taxa representative of three ecologically distinct lake types, Carbonate buffered - Oligodystrophic - Weakly buffered soft water. Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 2. Ecology, Diversity, Taxonomy. Koeltz Scientific Books. Königstein, Germany, 2:390 pp.
Specimens of S. alastos pictured and described on this page were collected from five ponds and small lakes in the Rocky Mountains of Montana and Colorado and the North Cascade Mountains of Washington. pH ranged from 6.73 to 6.98 and specific conductance measured 22 to 71 µS/cm. Sellaphora alastos was described from a river in eastern Canada (Hohn and Hellerman 1963) and also reported from an oligo-dystrophic lake in Finland (Lange-Bertalot and Metzeltin 1996).
Lake Caroline, Chelan County, Washington: home of Sellaphora alastos.
Credit/Source: Ryan Davis, Adventurers and Scientists for Conservation