• Category
  • Length Range
    6-18 µm
  • Width Range
    3.7-7 µm
  • Striae in 10 µm
    9-12 on rapheless valve, 24-30 on raphe valve
  • Synonyms
    Achnanthes oblongella Østrup
    Karayevia oblongella (Østrup) Aboal in Aboal, Alvarez-Cobelas, Cambra and Ector



Valves are elliptical-lanceolate to linear-elliptical. The raphe valve has a narrow linear axial area and a transversely rectangular or bow tie-shaped central area. The raphe is straight, without terminal fissures. The proximal and distal raphe ends are slightly expanded. The proximal raphe ends curve toward opposite sides internally. Striae on raphe valve are slightly radiate in the valve center and strongly radiate and curved at apices, 24-30 in 10 µm. The areolae openings are small, round. The rapheless valve has a narrow lanceolate axial area. The central area is usually not differentiated from the axial area, but sometimes two middle striae on one side of the valve are more distant from each than other striae. Striae on rapheless valve are broader than those on the raphe valve, punctate, parallel in the center and radiate at apices, 9-12 in 10 µm. Shortened marginal striae are often present. The openings of the areolae are apically elongated, internally areolae open into a shallow chamber.


Original Description

L. 0,057 mm., B. 0,006 mm. Epitheca: apical area narrow, 10 striae in 0,01 mm., finely transversely lineated. Hypotheca: striæ very fine, slightly curved. Central area narrow. Hypotheca of this small species highly reminds of Navicula Rotœana Grun. var. oblongella Grun. (V. H., Syn. tab. XIV,.fig. 21). But as I have seen both valves in situ, I am quite sure it is an Achnanthes.

  • Basionym
    Achnanthes oblongella
  • Author
    Østrup 1902
  • Length Range
    57 µm
  • Width
    6 µm
  • Striae in 10µm
    10 in "epitheca" (rapheless valve)

Original Images

Orig Ill  Karobl
Orig Descr  Karobl


Aug 09, 2020 - New combination

From February 2011 to August 2020, this taxon appeared as Karayevia oblongella (Østrup) Aboal in Aboal, Alvarez-Cobelas, Cambra and Ector. In 2017, Wetzel et al. recognized that this species does not fit within the generic description of Karayevia and transferred it to the genus Platessa. - M. Potapova

Cite This Page

Potapova, M. (2011). Platessa oblongella. In Diatoms of North America. Retrieved May 24, 2024, from https://diatoms.org/species/platessa_oblongella


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