Valves are linear with slightly convex sides. The ends are broadly rostrate, to subcapitate and rounded. The central area is large, with a rhombic fascia extending to the valve margin. The width of the fascia is variable among specimens. Four large, shallow depressions are present on the internal surface of the valve, containing ghost striae. The axial area continuously widens from the ends to form the large central area. Striae are radiate in the middle and become slightly convergent toward the ends. Longitudinal lines are absent. The raphe is lateral, with the outer fissure weakly undulate. The proximal raphe ends are small and placed relatively closely to one another. The length-to-width ratio is 4.5-6.5.


The specimens shown were collected from two sites: Beck's Canal in Little Miller's Bay, with water temperature 15 C, pH 8.37 and conductivity 436 µS. The pond on Highway 9 had a water temperature of 13.2 C, pH 7.97 and conductivity of 1022 µS. Both sites were near roads and high human disturbance.

Original Description

Outline linear, sides slightly convex, ends very broadly rostrate to subcapitate and broadly rounded, length 34-70 µm, breadth 10-12 µm, length-to-breadth ratio about 5.5 in medium size valves. Raphe lateral, the outer fissure very weakly undulate and proximally curved to the ventral side, central pores small, drop-like, close standing, terminal fissures large, ?-shaped. Axial area 1/4-1/3 the valve breadth, continuously widened from the ends to the rhombic central area which is differentiated, in the valve middle with a moderately broad assymentrical fascia. Striae 8-10/10 µm, radiate in the middle, slightly convergent towards the ends, longitudinal lines absent. The central area is accompanied by four large markings, the larger in the ventral side.

In the outline this taxon has some resemblance with the rhombarea group, whereas the broad axial area and the markings combine the taxon with the gibba group. Navicula parva sensu Grunow has a similar outline, however the axial area is much smaller.

  • Author
    Krammer 2000
  • Length Range
    34-70 µm
  • Width
    10-12 µm
  • Striae in 10µm

Original Images

Pinnularia Parvulissima Scan 1
Pinnularia Parvulissima Scan 2

Cite This Page

Sakaeva, A. (2013). Pinnularia parvulissima. In Diatoms of North America. Retrieved June 22, 2018, from


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