• Category
  • Length Range
    44-109 µm
  • Width Range
    13.5-26.0 µm
  • Striae in 10 µm
  • Reported As
    Cymbella cistula var. gibbosa (Patrick and Reimer 1975, p. 63, Plate 11, Figs 5-7)



Valves are dorsiventral, with broadly rounded apices. The dorsal margin is strongly arched. In larger valves, the ventral margin is concave with a distinctly gibbous center. In smaller valves, the ventral margin is somewhat convex to nearly flat. The axial area located just ventral to the valve mid line. The central area is small and elliptic. The raphe is lateral, becoming reverse-lateral near the proximal ends. Proximal raphe ends are deflected ventrally and terminate in slightly expanded pores. Three to seven stigmata are present on the ventral side of the central area. Striae are radiate throughout. Areolae are distinct in LM and number 16-21 in 10 µm.

Patrick and Reimer (1975) report similar specimens from Lake Michigan (pl. 11, figs 5-7) as Cymbella cistula var. gibbosa. That taxon was described by Brun (1895) from Lake Geneva, Switzerland and was later elevated to species rank (Meister 1912) as Cymbella gibbosa. That name, however, is a later homonym of a species described by Pantocsek (1901). Krammer (2002, p. 79) proposed that the Brun taxon represents initial cells of C. cymbiformis and is not related to C. cistula. We therefore conclude that the specimens shown here from Montana, and those reported by Patrick and Reimer from Lake Michigan probably belong to C. neocistula var. islandica and not to the Brun taxon.

Reimer comments that stigmata may also be present on the dorsal side of the central area, and that valves may be up to 26 µm wide (Patrick and Reimer 1975, p. 63).


This taxon is less widely distributed than C. neocistula. It has been collected from several lakes in Glacier National Park, Montana, including Lake Josephine in the Many Glacier area (photo below). In these lakes pH ranges from 7.59 to 8.04 and specific conductance ranges from 94 to 129 µS/cm. Patrick and Reimer (1975) illustrate similar specimens from Lake Michigan (Pl. 11, Figs 5-7). Krammer (2002) reports this taxon from Iceland and other nordic and subarctic regions, in oligotrophic waters with lower electrolyte content.

L  Josephine
Credit: Loren Bahls
Lake Josephine, Glacier National Park, Montana: home of Encyonema ventricosum

Original Description

Breadth larger [than the nominate variety], puncta coarser and more striae/10 µm. Length 64-114 µm, breadth 19-23 µm, striae 9-11/10 µm, puncta 13-16/10 µm.

  • Author
    Krammer 2002
  • Length Range
    64-114 µm
  • Width
    19-23 µm
  • Striae in 10µm

Original Images

Cymbella neocistula orig illus
Cymbella neocistula var. islandica orig descr

Cite This Page

Bahls, L. (2016). Cymbella neocistula var. islandica. In Diatoms of North America. Retrieved May 24, 2024, from https://diatoms.org/species/cymbella_cistula_var_gibbosa


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Cymbella neocistula var. islandica 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.