• Category
  • Length Range
    48-129 µm
  • Width Range
    9.7-10.1 (valve, excluding keels); 14.9-18.8 (valve, including keels); 32-42 (girdle view) µm
  • Striae in 10 µm
  • Synonyms
    Amphiprora alata (Ehrenb.) Kütz. 1844



Valves in valve view at the valvar plane are linear-elliptic to linear lanceolate with slightly concave sides and apiculate apices. Highly arched bilobate keels dominate the view in girdle aspect. The keels are strongly torsioned so that only one lobe is in focus at one time. In complete frustules in girdle view, diagonally opposing lobes lie at approximately the same level of focus. Lobes are flattened in large specimens and more rounded in smaller specimens. Several girdle bands are present. The junction line between the valve and the keel, like the outer edge of the keel, is flattened in larger specimens and more rounded in smaller specimens. The junction line is marked by an irregular series of dark spots. In valve view these spots can be seen as thickened siliceous ribs that frame a series of prominent swellings along the junction line. The swellings are approximately equal in size. Striae on the valve face continue onto the keel. Areolae on the valve face are very fine and number 26-30 in 10 µm within a stria. Areolae on the keel are much more prominent and number 12-15 in 10 µm within a stria.


Entomoneis alata occurs frequently in streams of the Northwestern Great Plains (Montana, North Dakota, South Dakota, Wyoming). In these waters the mean pH is 8.6 and the mean specific conductance is 4459 µS/cm. Sodium and sulfate are the dominant cation and anion, respectively. Common diatom associates of Entomoneis alata include Cymbella pusilla, Entomoneis paludosa, Biremis circumtexta, Navicula salinarum, Nitzschia reversa, Staurophora brantii, Nitzschia filiformis, Fallacia pygmaea, Pleurosigma delicatulum, and Navicula peregrina. There have been several reports of this species from across the United States in inland waters with elevated concentrations of electrolytes (Patrick & Reimer 1975).

Original Description

  • Basionym
    Navicula alata
  • Author
    Ehrenb. 1840

EMAP Assessment

EMAP Distribution

Entomoneis Alata 40
Map 40

Response Plots

Entomoneis Alata

Cite This Page

Bahls, L. (2012). Entomoneis alata. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/entomoneis_alata


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