• Category
  • Length Range
    10–16 µm
  • Width Range
    3.1-4.1 µm
  • Striae in 10 µm
  • Synonyms
    Achnanthes pusilla Grunow in Cleve and Grunow 1880
    Achnanthidium pusillum (Grunow) Czar. 1995



Valves linear or linear-elliptical with rounded ends, 3.1-4.1 µm wide, 10-16 µm long. Raphe valve with narrow axial area and with small round or irregular central area. Terminal raphe fissures absent. Raphe straight, filiform. Central raphe endings curved to opposite sides internally. Rapheless valve with narrow linear axial area without a central area or with a very small asymmetrical central area. Striae uniseriate, slightly radiate, one or two striae in the middle portion of the raphe valve are thicker than the rest, 20-24 in 10 µm. External openings of areolae are isodiametric or slightly elongated transapically. Each stria in the middle part of the valve contains 4-5 areolae. The valve mantle bears one row of areolae.


As other monoraphid diatoms, Rossithidium pusillum is only slightly motile. Coldwater, oligotraphentic species.

Original Description

Schaalen linear mit abgerundeten Enden. Querstreifen der Overschaale fast parallel, der Unterschaale schwach radial, die mittelsten entfernter und starker, 18-23 in 0.01 mm. Schaalen 0,013-0,017 mm. lang, 0.003-0,004 mm breit. Finshoe, Norwegen. Nordstedt.

  • Basionym
    Achnanthes pusilla
  • Author
    Grunow 1880
  • Length Range
    13-17 µm
  • Width
    3–4 µm
  • Striae in 10µm
    18-23 in 10 µm

Original Images

Achnanthes pusilla orig illus
Aulacoseira pusilla orig descr

Cite This Page

Potapova, M. (2009). Rossithidium pusillum. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/rossithidium_pusillum


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