Hohn and Hellerman 1963 Category: Nitzschioid
BASIONYM: Nitzschia biacrula Hohn and Hellerman 1963
SYNONYM(S): Nitzschia dissipata var. borneensis Hustedt and Simonsen 1987
Contributor: Kalina Manoylov - July 2010
Length Range: 36-65 µm
Width Range: 5.2-6.5 µm
Striae in 10 µm:
Valves linear to lanceolate with ends strongly beak-like. Length 36 to 64.5 µm, width 5.2 to 6.5 µm. Raphe appears to be nearly parallel to the apical axis in valve view. Near the valve terminus the raphe ends are deflected in opposite direction to one another. The raphe is positioned almost at the middle of the valve or displaced towards the margin, but it is never at the margin itself. Although the raphe is near the valve middle, the position shows hantzschiod symmetry rather than nitzschiod symmetry. Striae are not discernable. Fibulae are irregularly spaced, appearing box-like. The conopeum, a silicious covering above the valve surface, appears as a faint longitudinal line somewhat in the middle of the raphe. Fibulae 6-9 in 10 µm. Frustules are sigmoid in girdle view. Numerous girdle bands are present.
Note that Nitzschia biacrula is an earlier homonym of Nitzschia dissipata var. borneensis Hustedt et Simonsen (1987, page 59, plate 77, figs 8-16) and has nomenclatural priority. In 1921, Nitzschia dissipata var. borneensis was invalidly published (Hustedt in Schmidt et al. 1921, pl. 335, fig. 22-24). The taxon was later validated by Simonsen (1987), after the publication of Nitzschia biacrula.
Basionym: Nitzschia biacrula
Author: Hohn and Hellerman 1963
Length Range: 49.4-56.2 µm
Width Range: 5.3-7.8 µm
Striae in 10 µm:
Valva lineari-lanceolata, apicibus valide rostratis et sigmoidis. Carina leniter sigmoida, paene in media. Punctis carinae inaequalibus in magnitudinibus et amplitudinibus, 8-9/10 µ. Frustule sigmoido in conspectus cingulo. Striis non manifestis. Longitudo 49.4-56.2 µ. Latitudo 5.3-7.8 µ.
Valve linear-lanceolate, ends strongly beaked and sigmoid; keel slightly sigmoid, nearly median; keel puncta irregular in size and spacing, 8-9/10 µ; frustule sigmoid in girdle view; striae invisible; length 49.4-56.2 µ, width 5.3-7.8 µ.
This species is seldom found in valve view. In girdle view, although it strongly resembles Nitzschia dissipata (Kütz.) Grun. (K.Sv. Vet.-Acad. Handl. 17 (2): 90, 1880) it is easily distinguished by its sigmoid shape.
Specimen illustrated: GC. 44466, Type. Type locality: Potomac River, Md. Distribution: Type locality and Ridley Creek, Pa.
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.