• Category
  • Length Range
    18-40 µm
  • Width Range
    9-20 µm
  • Striae in 10 µm
    22-24 in center valve
  • Synonyms
    Achnanthes flexella (Kütz.) Brun



Frustules are strongly bent in girdle view with concave raphe valve and convex rapheless valve. Valves are elliptical-lanceolate with slightly drawn-out ends and deep mantles. Valve face has depressions along the margins. The raphe valve has a narrow axial area and a lanceolate-rhomboid central area. The raphe is straight or slightly sigmoid with terminal ends sharply turned to opposite directions. Rapheless valve has a narrow linear or slightly sigmoid axial area and a large rectangular or hexagonal central area. The striae are punctate, strongly radiate on raphe valve and slightly radiate on rapheless valve, 22-24 in 10 μm.


This diatom is small in size and typically grows attached to surfaces in a prostrate manner. Cells are only slightly motile and grow as single cells (they do not form colonies). In California, this taxon is characterized within the Biological Condition Gradient (BCG) of 2, which are highly sensitive species. It has been reported from streams of the west (EPA Western EMAP, USGS Regional Survey of California) and lakes of the northeast (EPA Northeast Lake Survey).

Original Description

CYMBELLA? FLEXELLA. Taf. 4. Fig. XIV, Taf. 6. Fig. VIII. (420/1). C. laevissima, mi¬nor, a latere secundario elliptica, subsigmoidea, apicibus parum productis obtusis, altero latere cur-vata, (genuflexa) dorso convexo, ventre concavo exciso, apice truncato. In Quellwasser bei Thun in der Schweiz! — Länge 1/55"'.

  • Basionym
    Cymbella flexella
  • Author
    Kütz. 1844
  • Length Range
    41 µm

Original Images

Orig Ill 1 1
Orig Ill 2

Cite This Page

Potapova, M. (2010). Eucocconeis flexella. In Diatoms of North America. Retrieved May 24, 2024, from https://diatoms.org/species/eucocconeis_flexella


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