• Category
  • Length Range
    104-147 µm
  • Width Range
    46-62 µm
  • Synonyms
    Navicula bifrons Ehrenb. 1834
    Surirella bifrons (Ehrenb.) Ehrenb. 1843
    Surirella biseriata var. bifrons (Ehrenb.) Hust. 1911



Valves are lanceolate and isopolar, with rounded, cuneate ends.

Porcae, the transapical ribs, are 1-3 μm wide, and number 8-12 in 50 μm. Porcae on either side of the valve are usually positioned opposite each other and become increasingly radiate at the apices. Short, robust spines resembling rose thorns cover the valve face, with a majority of the spines located on the porcae and central area. The central area is wide and lanceolate in shape. The well-developed alar wing is resolvable in girdle view. The raphe is situated atop the alar wing. Transapically, alar canals are twice as wide as porcae. Between the valve face and valve margin are fenestrae with ~4 fenestral bars in each window.

Valve outline of this taxon is variable from lanceolate (e.g., the largest specimen on this page) to rhombic, according to investigation of type material and Ehrenberg's original illustrations (Jahn et al. 2017). Mohamad et al. (2022) showed that clonal strains of surirelloid taxa can be highly variable in their valve outlines, while other features such as number of striae, costae, and fibulae were more stable. Additional studies with SEM and molecular data are needed to determine the range of morphological variability of this taxon from North America and if it is truly conspecific with those reported from other continents (e.g., Africa, Cocquyt 1998).


This taxon was observed in West Lake Okoboji, a glacially formed deep freshwater lake in northwest Iowa. It was present in small numbers in the top centimeter of lake sediment. In North America, it has also been reported from Adak Island, Alaska (Hein 1990).

Other reports include from Germany in the Lower Rhine River and lakes, including Lake Constance (Bodensee) near Lindau, Schollener See in Sachsen-Anhalt, Lake Starnberg (formerly known as Würmsee), as well as Lake Tanganyika, Africa (Krammer and Bertalot 1997, Cocquyt 1998).

Original Description

Discovered near Berlin between Conferven on May 10, 1832.

The form most closely related is the beautiful Navicula (Surirella) splendida, which is also only a little larger. The carapace of Surirella striatula is elliptical, about 1 times as long as wide. At Sur. splendida, seen from the back, it is long, ovoid, somewhat pointed in front, strongly rounded behind, about 3 times as long as wise. Seen from the side it is a long square, with rounded corners, wider behind than in front and somewhat constricted in the middle. At Sur. Bifrons, seen from the back, it is lanceolate, pointed in front and behind, 3 times long as wide; Long quadrangular seen from the side, with rounded corners equal width in front and behind. Without constriction, 3 times as long as wide. In both species observed by me it is very clear that the striation of the carapace takes place only at the four corners and that it is not external but internal. In S. splendida I counted 26 stripes in one of the 4 chafers that did not cause outer serrations of the rim. In S. bifrons I counted 21 stripes.

In the body lying on its side, one can very easily recognize 2 darker yellow-brown plates, which cover the dorsal and ventral sides, and 2 lighter, folded and jagged, more inwardly lying, yellowish organs, which have a jagged light-colored space lengthwise in leave the middle. At Sur. splendida has a lighter spot in the front pointed end on the dorsal side, in which mobile black ones organs are visible. This spot is visible at both ends in S. bifrons, but I could not see any moving organs in it. Also I saw at S. splendida many small, light-colored vesicles inside (stomach bubbles?), same in S. bifrons were not distinguishable. Both forms had distinct vigorous movement. Length 1/18’”

  • Basionym
    Surirella bifrons
  • Author
    Ehrenb. 1834
  • Length Range
    1/18'" µm

Original Images

Iconella bifrons orig illus
Iconella bifron orig desc

Cite This Page

Liebrecht, P. (2023). Iconella bifrons. In Diatoms of North America. Retrieved September 23, 2023, from https://diatoms.org/species/iconella-bifrons


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