Identification

Description

Valves are relatively broad, cymbelloid and semi-elliptic. Apices are bluntly rounded and weakly protracted. The dorsal margin is strongly arched; the ventral margin is slightly convex to nearly flat. The axial area is linear and a bit wider than the raphe. The central area is small and circular to elliptic in shape. A single large stigma is present between the proximal raphe ends. The raphe branches are lateral, becoming narrower near the proximal and distal ends. Proximal raphe ends terminate in bulbous central pores that are deflected slightly towards the ventral margin. Terminal raphe fissures are deflected dorsally at about 45º. Well developed porefields are present at both apices. Striae are radiate throughout. The dorsal and ventral striae in the central portion of the valve are variable in length. Areolae are very distinct in LM and number 10-12 in 10 µm. Areolae on the ventral side of the central area are elongate and triangular in shape.

This is a smaller, more compact form of C. mexicana with bluntly rounded and weakly protracted apices. It may occur in association with the nominate variety, but it is often the only variety of the species that is present.

Editor's note: Users should be aware that this variety may represent small forms of the nominate species. We appreciate documentation and feedback on the occurrence of this taxon in North America.

Autecology

Cymbella mexicana var. kamtschatica has been collected from several creeks and rivers in the Northern Rocky Mountains of Montana and Idaho. The pH of these waters ranges from 7.90 to 8.55 and specific conductance ranges from 61 to 608 µS/cm. It may occur in association with the nominate variety, but often not. This variety was described from fossil material collected in Kamtschatka and has also been reported from the Colorado River (Krammer 2002).

Clark Fork River
Credit: Realty-Northwest
Clark Fork River near Missoula, Montana: home of Cymbella mexicana var. kamtschatica

Original Description

  • Basionym
    Cocconema kamtschaticum
  • Author
    Grunow in A.Schmidt 1875
  • Length Range
    70-160 µm
  • Width
    25-32 µm
  • Striae in 10µm
    6-9

Original Images

Cymbella mexicana var. kamtschatica orig desc
Cymbella mexicana var. kamtschatica orig illus
Cymbella mexicana var. kamtschatica orig illus
Cocconema kamtschaticum orig descr

Cite This Page

Bahls, L. (2016). Cymbella mexicana var. kamtschatica. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/cymbella_mexicana_var._kamtschatica

Responses

The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Cymbella mexicana var. kamtschatica 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.