• Category
  • Length Range
    17-80 µm
  • Width Range
    3-4 µm



Frustules form fan-shaped colonies and are clavate in girdle view. Valves are linear-clavate and asymmetric to the transapical axis. Costae are present and run transversely across the valves. In many specimens illustrated here, the costae are only present towards the headpole, and are not present towards the footpole. A narrow sternum is present running the length of the valve. A single rimoportula is located near the headpole. Though rarely reported, Meridion species do possess a septum, and these were commonly seen in the material.

Williams (1985, p. 160) reports the breadth of M. circulare as 10-21 µm, while Patrick and Reimer (1966) give 4-8 µm.

Distribution: Meridion circulare is found across the US, in habitats flowing water and spring habitats.


Original Description

  • Basionym
    Echinella circularis
  • Author
    Grev. 1831

Cite This Page

Kociolek, P. (2011). Meridion circulare. In Diatoms of North America. Retrieved July 24, 2024, from https://diatoms.org/species/meridion_circulare


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