• Category
  • Length Range
    20-24 µm
  • Width Range
    13-19 µm
  • Striae in 10 µm



Valves are elliptic. The raphe valve has a narrow axial area and a vary small circular central area, or no distinct central area at all. The raphe is straight and filiform. The distal raphe ends are straight and expanded externally. The proximal raphe ends are externally straight and slightly expanded. Striae are radiate and interrupted by a hyaline rings positioned close to the valve margin. Areolae are usually well distinguished under LM, and number15-25 in 10 µm. Areolae are arranged into longitudinal rows. The rapheless valve has a linear to linear-lanceolate axial area and radiate striae. Areolae are much smaller in the raphe valve than in rapheless valve, but in both valves areolae are smaller near the axial area. Areolae become conspicuously larger toward the valve margin.

Original Description

The rapheless valve is somewhat similar to Cocconeis intermedia Herib. and Perag. It differs from this in that the puncta which make up the striae in this new species become progressively heavier and longer as they approach the valve margin, 16 striae in 10 μ in the middle (as measured along the raphe) and 12 striae in 10 μ at the margin. The raphe valve has the same striae count, but the striae are finely punctate throughout. An interruption, as found in Cocconeis placentula Ehr. and its varieties is present, but the lower striae number in this species removes it from the Cocconeis placentula complex.

  • Author
    J.H.Wallace 1960
  • Length Range
    23-24 µm
  • Width
    13-19 µm
  • Striae in 10µm
    16 along raphe, 12 near margin

Original Images

Cocconeis fluviatilis orig illus
Orig Desc  C Fluviatilis
Original text and images reproduced with permission by Academy of Natural Sciences of Philadelphia.

Citations & Links


  • Index Nominum Algarum
  • North American Diatom Ecological Database
    NADED ID: 16010

Cite This Page

Potapova, M. (2010). Cocconeis fluviatilis. In Diatoms of North America. Retrieved May 28, 2024, from https://diatoms.org/species/cocconeis_fluviatilis


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