• Category
  • Diameter
    4.3-9.5 µm
  • Striae in 10 µm
    8-12 based on circumferential count
  • Synonyms
    Stephanodiscus hantzschii fo. parva Grunow in Cleve and Grunow 1880



Valves are disc-shaped with a flat to slightly undulate face and shallow mantle. A single fultoportula is present in a slightly eccentric position in the center valve. Areolae are present across the valve face, weakly organized into rows at the valve center and forming more distinct fascicles toward the valve margin. Fascicles are uniseriate in the valve center, and may become biseriate at the valve face/mantle interface. The number of fascicles ranges from 17-31 per valve and decreases with valve diameter. Areolae are distinct and occur at 18-20 in 10 µm. Small spines are present on each interfascicle, at the valve margin.

The relation between fascicle number and valve diameter can be expressed as total number of fascicles = 0.78 * (diameter) + 5.12. For example, measures of diameter and fascicle count, respectively, are 9.3,31; 7.4,24; 4.5,14.


Stephanodiscus parvus is most common in eutrophic lakes Erie and Ontario under conditions of high total phosphorus and moderate chloride concentration (Stoermer et al. 1978, Stoermer 1978, Stoermer and Håkansson 1984, Reavie and Kireta 2015). This taxon has also been reported from from the St. Lawrence River, with rare abundances from epilithic and epiphytic habitats, and greater abundant in sediment cores (Reavie and Smol 1998)

Stparvus  Distribution
Credit: USGS/Biodata
The record of Stephanodiscus parvus in streams and rivers of the continental United States.

Original Description

Valves circular, almost flat 5-11 µm in diameter. Ornamentation of the valve surface consisting of barely resolvable puncta arranged in biseriate fascicles, 13-15 in 10 µm, each fascicle separated by a distance interfascicle. Each interfascicle subtended by a well developed spine. Marginal strutted processes occur directly below every 3rd to 6th spine. One eccentric strutted process on the valve face present.

Valve ornamentation occurs in a coarsely and a finely structure form. In the coarsely structured form the puncta are arranged in biseriate, straight fascicles, becoming uniseriate or disorganized towards the center of the valve. In the finely structured form the puncta are also arranged in biseriate, straight fascicles, becoming disorganized towards the center where the puncta are grouped in a rosette0like configuration.

  • Author
    Stoermer and Håk. 1984
  • Length Range
    5-11 µm
  • Striae in 10µm
    13-15 fascicles in 10 µm

Original Images

Stparvus Original  Image
Stparvus Original Description

Cite This Page

Burge, D, and Edlund, M. (2016). Stephanodiscus parvus. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/stephanodiscus_parvus


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