• Category
  • Length Range
    30.2-66.2 µm
  • Width Range
    8.0-13.7 µm
  • Striae in 10 µm
    19-23 dorsal at center; 22-26 dorsal at ends



Valves are semi-elliptical and strongly dorsiventral. The dorsal margin is highly arched. The ventral margin is usually weakly concave, but is slightly tumid near the central nodule in larger specimens and nearly straight in smaller valves. Valve ends are subcapitate, ventrally curved and slightly protracted. The raphe is positioned near the ventral margin. The raphe branches are typically straight, but may be slightly curved dorsally from the poles toward the central area. Proximal raphe ends are expanded and dorsally deflected; distal raphe ends have a short dorsal deflection. The axial area is a narrow, often arched or semi-circular hyaline area on the dorsal side of the central nodule. In larger valves (> 60 µm), the hyaline area may be greatly expanded. Dorsal striae are finely punctate, with dash-like areolae that radiate throughout. Distinctly thickened virgae and widely-spaced striae are present between the proximal raphe ends. Ventral striae are short and difficult to see in LM, especially in the in central area.

Under the SEM, short striae can be seen on the ventral margin (Kociolek et al. 2014).


Halamphora subcapitata was collected from modern shallow (~3 m water depth) sediment surfaces from Foy Lake, Montana. Foy Lake has a slightly elevated conductivity (1.1 mS/cm).

Original Description

Valves with smoothly curved, convex dorsal margin. Ventral margin slightly convex. Ends protracted narrowly, rostrate to capitate. Length 31- 50 μm . Breadth 8- 11 μm. Axial area linear or linear-lanceolate, wide. Central area asymmetric to rounded formed by an interruption of the ventral striae and more or less shorten striae on the dorsal side. External proximal raphe ends rounded; external distal raphe ends curving dorsally over the last two dorsal striae. Dorsal striae radiate less numerous and more widely spaced at mid-valve, 19- 23/10 μm with dash-like puncta. Ventral striae composed of short dashes 26-30/10 μm.

  • Author
    Bennett and Kociolek 2014
  • Length Range
    31-50 µm
  • Width
    8-11 µm
  • Striae in 10µm
    19-23 at dorsal ends, more widely spaced at mid-valve; 26-30 ventral mid-valve

Cite This Page

Stone, J. (2015). Halamphora elongata. In Diatoms of North America. Retrieved July 23, 2018, from https://diatoms.org/species/halamphora_elongata


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