• Category
  • Length Range
    11.3-15.6 µm
  • Width Range
    2.7-3.3 µm
  • Striae in 10 µm
  • Reported As
    Stauroneis gracillima (Hustedt 1943, p. 154, figs 21-23)
    Stauroneis gracillima (Krammer and Lange-Bertalot 1986, p. 248, pl 90, figs 28-30)
    Nupela gracillima (Lange-Bertalot 1993, p. 158)



Valves are linear-lanceolate and weakly dorsiventral, with capitate apices. Valve margins are usually straight and parallel. Some specimens may have a slightly convex ventral margin, while others may have a concave ventral margin. The axial area is very narrow. The central area is an asymmetric, nearly rectangular fascia that is a bit wider on the dorsal side of the valve. SEM images show that the central area does not quite reach the valve margins and is bordered by short striae. A filiform raphe, with tear-shaped proximal raphe ends is present on both valves. Striae cannot be resolved under light microscopy.

Hustedt described two taxa - Navicula tenuicephala (from a lake in Swedish Lapland) and Stauroneis gracillima (from a lake in the central Alps) which I considered to be conspecific and present here as Nupela tenuicephala.


The specimens pictured on this web page are from a pond in the Mexican Cut Nature Preserve in the Rocky Mountains of Colorado. Nupela tenuicephala has also been recorded from ponds and small lakes in the mountains of Montana, Oregon and Washington. In two of these waters, pH measured 5.88 and 6.30 and electrical conductance measured 3 and 7 µS/cm.

Lower  Snowy  Lake
Credit: Craig Weiland, Adventurers and Scientists for Conservation
Lower Snowy Lake, North Cascades, Skagit County, Washington: home of Nupela tenuicephala

Original Description

  • Basionym
    Navicula tenuicephala
  • Author
    Hust. 1942

Original Images

Naviculatenuicephala Origimag001
Naviculatenuicephala Origimag002
Stauroneisgracillima Origimag001
Naviculatenuicephala Origdesc001

Cite This Page

Bahls, L. (2016). Nupela tenuicephala. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/nupela_tenuicephala


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Nupela tenuicephala 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.