(W. Smith) Krammer 1997 Category: Asymmetrical biraphid
BASIONYM: Cymbella aequalis W. Smith in Greville 1855
REPORTED AS: Cymbella aequalis (Krammer and Lange-Bertalot 1986, p. 325, pl. 134, figs. 1-3)
Contributor: Loren Bahls - May 2013
Length Range: 22-41 µm
Width Range: 5.6-7.6 µm
Striae in 10 µm: 12-16 at the valve center, 18-20 near the ends
Valves are weakly dorsiventral and lanceolate with subrostrate apices deflected slightly to the ventral side. Valve shoulders are lacking. The axial area is narrow. The central area is small, formed by the two opposing shorter and more widely spaced central striae. The raphe is lateral with weakly inflated proximal ends that are deflected toward the dorsal margin. Distal raphe ends are hooked toward the ventral margin. Striae are weakly radiate except at the valve center and near the apices, where they are parallel. Areolae are very fine and difficult to resolve in LM.
Basionym: Cymbella aequalis
Author: W. Smith in Greville 1855
Length Range: µm
Striae in 10 µm:
Cymbella aequalis, W. Sm. Pl. IX. fig. 4. Length 0014”
A very distinct new species, so nearly symmetrical as to be liable at a hasty glance to be taken for a Navicula. There is however a curve at the shortly produced, obtuse extremities. The striae are fine, but not very close. This form was abundant in one gathering only, composed of coarse black peaty mud extremely difficult to clean.
Bahls, L. (2013). Encyonopsis from western North America: 31 species from Alberta, Idaho, Montana, Oregon, South Dakota, and Washington, including 17 species described as new. Northwest Diatoms, Volume 5. The Montana Diatom Collection, Helena, 46 pp.
Greville, R.K. (1855). Report on a collection of Diatomaceae made in the district of Braemar by Professor Balfour and Mr. Gerge Lawson. Annals and Magazine of Natural History, 2nd series, 15:252-261.
Krammer, K. (1997). Die cymbelloiden Diatomeen. Eine Monographie der weltweit bekannten Taxa. Teil 2. Encyonema part., Encyonopsis and Cymbellopsis. Bibliotheca Diatomologica 37:1-469.
Krammer, K. and Lange-Bertalot, H. (1986). Bacillariophyceae. 1. Teil: Naviculaceae. In: Ettl, H., J. Gerloff, H. Heynig and D. Mollenhauer (eds.) Susswasserflora von Mitteleuropa, Band 2/1. Gustav Fisher Verlag, Jena. 876 pp.
Encyonopsis aequalis is widely distributed and locally abundant in lakes throughout the Northern Rockies and North Cascade Mountains (Bahls 2013). These lakes are slightly alkaline (pH 7.0-7.5) with low specific conductance (10-60 µS/cm).
Summit Lake, Waterton Lakes National Park, Alberta: home of Encyonopsis aequalis.
Credit/Source: Barb Johnston, Parks Canada.