• Category
  • Length Range
    19-36 µm
  • Width Range
    6.9-9.0 µm
  • Striae in 10 µm
    9-12 in the center valve, 13-14 at the ends
  • Reported As
    Cymbella excisa (Krammer 2002)



Valves are strongly dorsi-ventral, with subrostrate to rostrate apices. The dorsal margin is strongly arched, whereas the ventral margin is slightly convex or flat, often excised. The axial area is narrow, linear. The central area is very small or not distinct. One stigma is present at the end of the middle striae. The proximal raphe ends have central pores that curve to the ventral side. The raphe is lateral, becoming filiform near the distal end. Striae are slightly radiate. The areolae number 25-30 in 10 μm.

Note that this concept of Cymbella affinis is based on Kützing's type material examined by Reimer (see image below) and by Tuji (2007) and is different from the concept of Krammer (2002). Krammer examined material labeled C. affinis in W. Smith's collection within the Van Heurck collection, Antwerp, which contains C. tumidula Grunow. Therefore, Krammer claimed that these two species are synonymous and the name C. affinis has to be applied to diatom so far known as C. tumidula. Reimer's (below) and Tuji (2007) photographs of the type material of C. affinis, show, however, that Krammer's decision is incorrect, while C. affinis and C. excisa are conspecific. Kützing applied the name C. affinis to specimens without excision and C. excisa to specimens with excised ventral margin.

Original Description

  1. CYMBELLA AFFINIS. Taf. 6. Fig. XV. (420/1). C. minuta, utrinque obtusiuscula, dorso elatiori, ostiolis terminalibus majoribus hyalinis, latere primario majori elliptico-oblongo; striis transversalibus distinctis in 1/100 ''' 19. Cocconema Fusidium Ehrenb.? Inf. 1838. p. 226. — Amer. Taf. II. 1. 35. 11. 21.? — Cymbella ventricosa De Brébisson! (ex specim.) Falaise: De Brébisson! (Herb. Binder.) Schleswig: Herb. Binder! — Central-Amerika? — Fossil in schwedischem Bergmehl. — Länge 1/85'''.
  • Author
    Kütz. 1844

Original Images

Cymbella affinis orig illus
Reimer  Cymbella Affinis  Bm18530 1
Reimer  Cymbella Excisa 18543
Cymbella affinis orig descr

Cite This Page

Potapova, M. (2011). Cymbella affinis. In Diatoms of North America. Retrieved July 15, 2024, from https://diatoms.org/species/cymbella_affinis


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