• Category
  • Length Range
    30-65 µm
  • Width Range
    11.0-15.7 µm
  • Striae in 10 µm
  • Reported As
    Anomoeoneis sphaerophora f. 1 PISCES (Cumming et al. 1995, p. 34, plate 15, figs 1-9)
    Anomoeoneis sphaerophora (Schoeman and Ashton 1982, p. 86, figs 9-24)



Valves are lanceolate with rostrate to subrostrate apices. Axial area and raphe branches are narrow and straight. The central area is asymmetric and variable in size. The larger side of the central area is wedge-shaped and extends to the valve margin. The smaller side of the central area is round and typically bordered by a series of short striae at the valve margin. The central area contains faint ghost striae. The raphe is weakly lateral with tear-drop shaped proximal pores that are deflected slightly to one side. Terminal raphe fissures are bent sharply to the same side. Striae are radiate, becoming parallel then convergent at the apices. Lateral spacing of areolae is highly variable except along the valve margins.

This taxon is one of several new forms and varieties of Anomoeoneis sphaerophora described by Müller (1900, Tafel XII, Figs 1-13) from El Kab, Egypt. These include forms curta, elongata, truncata and rostrata, and varieties elliptica and guentheri. Conspicuously, Müller's illustrations do not include a typical elliptic valve of A. sphaerophora with capitate apices, which suggests that his forms and varieties represent a different species.

The taxon presented here from lakes in Montana has similar valve morphology as the type specimens of A. sphaerophora f. rostrata (figs 3, 4, 5), but has smaller valves and denser striae. However, the Montana specimens are encompassed in size by the other forms and varieties described by Müller, which likely all belong to the same species. For now, we report the Montana specimens here as A. sphaerophora f. rostrata, anticipating that it will be described in the future as a new species.


Anomoeoneis sphaerophora f. rostrata has been collected from a slough along the Milk River in northern Montana and from two glacially-scoured lakes in the prairie pothole region of northeastern Montana. One of these lakes (White Lake, Sheridan County) has a specific conductance of 87,000 µS/cm and a pH of 10.00. The other lake (Gaffney Lake, Sheridan County) has a specific conductance of 10,500 µS/cm and a pH of 9.60. Cumming et al. (1995) report this taxon (as. A. sphaerophora f. 1 PISCES) from saline lakes in southern British Columbia, Canada.

Schoeman and Ashton (1982) published a size-reduction series of this form (reported as A. sphaerophora) from a salt pan in South Africa, where sodium and chloride were the dominant ions. Their specimens range in width from 10 to 16 µm, which is comparable to Montana specimens and narrower than the nominate variety. Given the chemistry of the Montana, British Columbia and South Africa habitats, it is evident that A. sphaerophora f. rostrata can tolerate much higher concentrations of dissolved salts than the nominate variety.

Anomoeoneis Sphaerophora Rostrata
Credit: Loren Bahls
Anomoeoneis sphaerophora var. sphaerophora (top row) compared to A. sphaerophora fo. rostrata (bottom row)
Anomoeoneis Plate 1 Rostrata
Credit: Loren Bahls
Anomoeoneis taxa from western North America. Anomoeoneis sphaerophora fo. rostrata is shown in fig. 4.

Original Description

Anomoeoneis sphaerophora (Kütz.). Pfitzer.
Forma a, rostrata. Tafel XII, Figur 3, 4, 5; Seh. A. t. 49,51.
Valvarseite lanzettlich, Seitenlinien nach den Apices gleichmassig
abfallend, vor denselben stärker eingebogen. Apices
schmaler, schnabelförmig und länger vorgezogen, abgerundet oder
abgestutzt. Rhaphe gerade, die apicalen Enden gleichseitig nach
rechts verbogen. Axiale Area mittetbreit, näher den Apices enger.
Begleitlinien grade. Hellere Längsstreifen breiter, rechts annähernd
sichelförmig, links neben dem Centralknoten zu einem hellen Fleck
erweitert, der den Rand fast erreicht. Striae in der Mitte radial,
näher den Apices divergirend, 15•16 in 10 ¡n. Punkte kräftig, in
apicaler Richtung gewellte Linien bildend. Pleuraseite linear mit
abgerundeten Ecken, die Seiten schwach gewölbt. Lg. 52•92 /<,
lat. 15•25 ¡u.
Figur 4 mit stärker ausgebildeten transapicalen Furchen.
Wohnt in El Kab.
Eine kleinere Form bildet A. Schmidt, Atlas, t. 49,52 als Nav.
biceps Ehr. ab.

  • Author
    O. Müller 1900
  • Length Range
    20-92 (all forms and varieties) µm
  • Width
    11-25 (all forms and varieties) µm
  • Striae in 10µm
    15-16 (all varieties and forms)

Original Images

Mueller 1900 Anomoeoneis Sphaerophora Varieties
Anomoeoneis Sphaerophora Rostrata Orig Descr

Cite This Page

Bahls, L. (2018). Anomoeoneis sphaerophora f. rostrata. In Diatoms of North America. Retrieved February 16, 2019, from https://diatoms.org/species/anomoeoneis-sphaerophora-rostrata


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Anomoeoneis sphaerophora f. rostrata 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.