(Krasske) Mann 1990 Category: Asymmetrical biraphid
BASIONYM: Cymbella obscura Krasske 1938
REPORTED AS: Cymbella obscura (Krammer and Lange-Bertalot 1986, p. 306, figs 119:17-20) | Encyonema obscurum (Krammer 1997, p. 107, figs 28:1-8, 29:1-13, 30:1-15, 31:1,2, 33:1-5,14-20 )
Contributor: Loren Bahls - June 2016
Length Range: 18-28 µm
Width Range: 6.4-7.5 µm
Striae in 10 µm: 12-16
Valves are strongly dorsiventral with rostrate to subcapitate apices. Apices are oriented almost laterally such that the junction between the dorsal margin and the apex is concave. The dorsal margin is strongly arched. The ventral margin is slightly convex. The axial area is very narrow. The central area is a slightly wider continuation of the axial area. The raphe is filiform. Proximal raphe ends are deflected dorsally and terminate with slightly inflated central pores. Terminal raphe fissures are deflected ventrally. Striae are radiate on the dorsal side, a bit farther apart at the valve center than toward the apices. The median stria on the dorsal side meets the central area with a single isolated areola. The very short striae on the ventral side are radiate, then parallel, and finally convergent at the apices. Areolae in the striae are very fine and difficult to resolve in LM.
Basionym: Cymbella obscura
Author: Krasske 1938
Length Range: 24-27 µm
Width Range: 7.0-7.5 µm
Striae in 10 µm: 10-16
Krammer, K. (1997). Die cymbelloiden Diatomeen. Eine Monographie der weltweit bekannten Taxa. Teil 1. Allgemeines und Encyonema. Bibliotheca Diatomologica 36: 1-382.
Krammer, K. and Lange-Bertalot, H. (1986). Bacillariophyceae. 1. Teil: Naviculaceae. In: Ettl, H., J. Gerloff, H. Heynig and D. Mollenhauer (eds.) Süsswasserflora von Mitteleuropa, Band 2/1. Gustav Fisher Verlag, Jena. 876 pp.
Krasske, G. (1938). Beiträge zur Kenntnis der Diatomeen-Vegetation von Island und Spitzbergen. Archiv für Hydrobiologie 33:503-533.
Lange-Bertalot, H., Kulbs, K., Lauser, T., Norpel-Schempp, M. and Willmann, M. (1996). Diatom Taxa introduced by Georg Krasske: Documentation and Revision. Iconographia Diatomologica (H. Lange-Bertalot, ed.), Vol. 3, Koeltz Scientific Books, Konigstein, 358 pp.
Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.
This taxon was described from material collected in Spitsbergen, Norway. Krammer and Lange-Bertalot (1986) report it as a “nordic-alpine” species found in lakes of subalpine regions and the Lower Alps. The specimens shown on this web page were collected from Lake Josephine, a subalpine lake in Glacier National Park, Montana. At the time of collection, pH in Lake Josephine measured 7.59 and specific conductance was 94 µS/cm.
Lake Josephine, Glacier National Park, Montana: home of Encyonema obscurum
Credit/Source: Loren Bahls