• Category
  • Length Range
    36-64.5 µm
  • Width Range
    5.2-6.5 µm
  • Synonyms
    Nitzschia dissipata var. borneensis Hust. and Simonsen 1987



Valves are linear to lanceolate with ends strongly beak-like. The 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.


Original Description

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.

  • Author
    M.H.Hohn and Hellerman 1963
  • Length Range
    49.4-56.2 µm
  • Width
    5.3-7.8 µm

Original Images

H And  H  Ni  Ni Biacrula Text
H And  H  Ni  Ni Biacrula Drawing

Cite This Page

Manoylov, K. (2010). Nitzschia biacrula. In Diatoms of North America. Retrieved July 23, 2018, from https://diatoms.org/species/nitzschia_biacrula


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Nitzschia biacrula from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.