• Category
  • Length Range
    48-67 µm
  • Width Range
    16-18 µm
  • Striae in 10 µm
  • Synonyms
    Cocconema tumidum Bréb. ex Kütz. 1849



Valves are strongly asymmetric to the apical axis. Apices are strongly protracted. The ventral margin is slightly gibbous. The raphe is lateral. The proximal raphe ends are expanded into distinct pores. Externally, the pores are slightly deflected to the ventral side of the valve. The distal raphe fissures are deflected to the distal side, and clearly visible at the apical porefields. The sternum is narrow, and expands slightly near the midvalve. The central area is large and asymmetric. A large stigma is present on the ventral side of the central area. The striae are coarse, radiate, and irregularly bent. Prominent apical porefields are present.


Cymbella tumida is widely distributed across the United States, although it does not typically reach high abundance. It is found in both rivers and lakes, across a broad range of condition.

Original Description

C. tumidum. Brébisson in litt. – C. minus lunare, apicibus obtusis parum productis, altero latere lanceolato, apice lato truncato; striis transversis in 1/100‘‘‘ parte 16; stipite elongato filiformi simplici. – long. Cymbellar. 1/50 - 1/40‘‘‘. – Prope Mortain in Gallia legit amic. De Brébisson. (No. 289.) (v. s.)

  • Basionym
    Cocconema tumidum
  • Author
    Bréb. ex Kütz. 1849

Original Images

Cocconema tumidum orig descr

Cite This Page

Potapova, M. (2019). Cymbella tumida. In Diatoms of North America. Retrieved July 13, 2024, from https://diatoms.org/species/cymbella_tumida


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