• Category
  • Length Range
    19.4-37.5 µm
  • Width Range
    13-21 µm
  • Striae in 10 µm
  • Synonyms
    Odontidium glans (Ehrenb.) Kütz.



Valves are elliptic-lanceolate with a large central inflation and rounded to pointed apices. Thick transapical costae are mostly primary and evenly spaced at 2-3 in 10 µm. The striae are faint compared to the costae and are slightly radiate, more so toward the valve margins. Areola density is 21-27 in 10 µm. The axial area is narrow and linear, sometimes with poorly defined margins. Copulae contain septa that extend approximately 1/4 - 1/3 of the length of the valve. The above images were taken from populations from the Pacific Northwest and did not have rimoportulae, but 1-2 have been found on valves from European populations (Williams 1987).

Tetracyclus glans, T. rupestris and T. emarginatus comprise the three extant species within the genus Tetracyclus, which includes a large number of extinct species (Williams, 1987). North American T. glans valves are smaller than those observed in European populations (Williams 1987).

Tetracyclus lacustris is a later synonym for T. glans. Although T. lacustris is commonly used, T. glans is the correct name, by priority. Ehrenberg (1838) described the taxon first (as Navicula? glans). Later, Ralfs (1843) described the same organism as T. lacustris. See Williams (1989) and Williams (1996) for detail.


This taxon has been found throughout the west in cool, oligotrophic waterbodies, particularly growing in moist zones in association with mosses and liverworts (Bishop and Spaulding, 2015).

The specimens here are from the Snoqualmie River in the Central Cascades and from H.E. Sovereign’s collections (California Academy of Sciences) from Lake Ozette, on the Olympic Peninsula, both in Washington state. Tetracyclus glans was found in both locations with other araphid taxa, including Tabellaria flocculosa, Odontidium mesodon, Odontidium hyemale, and Meridion circulare. Tetracyclus glans also co-occurred in the Cascade samples with a new species of Tetracyclus.

Original Description

  • Basionym
    Navicula? glans
  • Author
    Ehrenb. 1838
  • Length Range
    26.4-52.8 µm

Original Images

Tetracyclus Glans Basionym

EMAP Assessment

EMAP Distribution

Tetracyclus Glans   Ehrenberg   Mills 40
Map 40

Response Plots

Tetracyclus Glans   Ehrenberg   Mills

Citations & Links



Cite This Page

Bishop, I. (2014). Tetracyclus glans. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/tetracyclus_glans


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