• Category
  • Length Range
    54-74 µm
  • Width Range
    11.5-14.0 µm
  • Striae in 10 µm
    28-30 in the center valve, 27-28 at the ends



Valves rhomboid with slightly constricted apices. The length to breadth ratio is highly variable. Longitudinal ribs and raphe are noticeably curved, giving the species an asymmetric appearance. Longitudinal striae, which are comprised of oval or lanceolate areolae, are present but are very wavy and sometimes disjointed. Striae do not circumradiate the poles. The external raphe ends are T-shaped. Internally, areolae are occluded. The longitudinal ribs and helictoglossae fuse to form a porte-crayon that is somewhat weak in size and shape.


Original Description

Valves are elliptic-lanceolate with shallow mantles and broadly rounded apices (Figs. 51–55 and 60). Striae are parallel over most of the valve face and absent at the poles. The lack of striae around the apices is readily observed with LM (Figs. 57–59). The areolae are not aligned between neighboring striae, forming zig-zagged rows along the apical axis (Figs. 51–59). The axial area and ribs aligning the raphe are bowed or curved between the central nodule and the ends of the valve (Figs. 51–55). The raphe ribs are unevenly fused in the center of the valve forming an asymmetric central nodule (Figs. 56 and 62). The side of the central nodule aligned with the convex side of the axial region is straighter and less swollen than the concave side. As a result, a distinct figure-of-eight design is not formed. The region between the proximal raphe fissures is thickened internally (Figs. 61–62). On the external surface, the central area is not expanded. The helictoglossae are long, linear, and fused at the base with the raphe ribs to form a portae-crayon structure that terminates close to the ends of the valve (Figs. 57–59). The raphe is bowed, filiform, with T-shaped proximal and distal fissures (Figs. 61 and 64). The areolae open externally as circular pores or elongated slits, the latter of which are aligned with the apical axis (Figs. 61, 63, and 64). Internally, the areolae are larger, circular and covered with a slightly raised and perforated hymen cover (Fig. 61). Four to six girdle bands can be found per frustule. The girdle bands are open, tweezer-shaped, and become expanded along the valve to form an enclosed cylindrical-shaped canal (Figs. 62–65). One or two rows of unoccluded areolae align the pars exterior of the girdle band (Figs. 63 and 64). The internal surface, on the side of the canal aligning the cell membrane, consists of a single row of narrow and elongated areolae each with a hymen covering (Fig. 65). Valves range in size from 45–83 µm long, 10–18 mm wide, and have a striae density of 28–30/10 µm.

  • Author
    Siver, Pelczar, and Hamilton 2009
  • Length Range
    45-83 µm
  • Width
    10-18 µm
  • Striae in 10µm

Original Images


Cite This Page

Graeff, C. (2012). Frustulia inculta. In Diatoms of North America. Retrieved April 21, 2024, from https://diatoms.org/species/frustulia_inculta


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