• Category
  • Diameter
    9.1-15.3 µm
  • Striae in 10 µm
    10-14 fascicles based on circumferential density

Identification

Description

Valves are small, with a concentrically undulate face and an annulus in the valve center. Areolae are difficult to resolve in LM. In the central area, areola are weakly organized near the annulus and then become organized into fascicles toward the margin. Fascicles are uniseriate near the valve center and become multiseriate near the margin. The number of total fascicles ranges from 26 to 55 and decreases with valve diameter. One to 3 central fultoportulae may present.

Cyclostephanos tholiformis and C. delicatus are indistinguishable in LM and they co-occur (Håkansson and Kling 1990). According to Håkansson and Kling, C. tholiformis is distinguished by one to three central fultoportula, interfascicles that branch on the mantle interior, marginal fultoportulae beneath every third to fourth spine and two satellite pores at each fultoportula. In contrast, C. delicatus has only one central fultoportula, internal fascicles on the mantle are non-branching, marginal fultoportulae occur beneath every fourth to sixth spine and three satellite pores at each fultoportula.

Autecology

Cyclostephanos tholiformis was described from Lazy Lagoon on West Lake Okoboji, Iowa. The planktonic algal assemblage of this canal was characterized as hypereutrophic (Stoermer et al. 1987).

Cyclostephanos Tholiformis1
Credit: USGS BioData
Distribution of Cyclostephanos tholiformis in rivers of the continental U.S. based on the National Water Quality Assessment program. Retrieved 03 June 2015.
Cyclostephanos Tholiformis2
Credit: USGS BioData
Distribution of Cyclostephanos tholiformis in rivers of Alaska based on the National Water Quality Assessment program. Retrieved 03 June 2015.

Original Description

Living cells occur singly or in short colonies. Frustules circular in valve view; short, cylindrical in girdle view. Valve face raise or depressed in the centre, marked with radial fascicles of fine punctate striae, separated by obvious interfascicles. Interfascicular ribs single on the valve face, branching on the margin of the valve. Valves from 7 to 10 µm in diameter, fascicles 12 to 13 in 10 µm. Spines occur on each thickened interfascicle near the valve face-valve mantle junction. A rimoportula (sic, this should say "a marginal fultoportula") occurs below every third or fourth spine. One, rarely two or three, fultoportulae occur eccentric to the valve centre. A single rimoportula with sessile internal labium and inconspicuous external opening occurs on a rib branch on the valve mantle.

  • Author
    Stoermer, Håk. and E.C.Ther. 1987
  • Length Range
    7-12 µm

Original Images

Cyclotella tholioformis orig illus
Cyclostephanos tholiformis orig descr

Cite This Page

Burge, D, and Edlund, M. (2015). Cyclostephanos tholiformis. In Diatoms of North America. Retrieved February 16, 2019, from https://diatoms.org/species/cyclostephanos_tholiformis

Responses

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