• Category
  • Length Range
    77-153 µm
  • Width Range
    11-18 µm
  • Striae in 10 µm
    transverse 18-20; longitudinal 18-22
  • Synonyms
    Navicula acuminata (Kütz.) Kütz. 1844
    Pleurosigma acuminatum (Kütz.) Grunow 1860
  • Reported As
    Gyrosigma spencerii (Patrick and Reimer 1966, p. 315, pl. 23, fig. 4.)



Valves are slender and sigmoid in outline, smoothly tapering to acutely rounded ends. The central area is small and longitudinally elliptical. The raphe is central and straight for half its length, except near distal ends where it follows a sigmoid shape and is slightly eccentric toward each convex side. Proximal raphe ends project into the central area and curve in opposite directions. The axial area is narrow. Areolae are uniseriate and punctate, except near margin where they appear more lineolate. Transverse and longitudinal striae are fine and appear equal in visibility. Transverse striae on either side of central area are very slightly radiate, with the remaining transverse striae parallel to one another, perpendicular to the raphe, and equidistant. Longitudinal striae are equidistant and follow a sigmoid shape, curving slightly toward the valve margin on either side of central area. Smaller specimens appear slightly less sigmoid and more linear-lanceolate.

Gyrosigma acuminatum has been referred to as G. spencerii in instances where valve lengths exceed 140 µm and are very slender. Sterrenburg (1995) compared type material for both species from different regions and reports that longitudinal and transverse stria density, longitudinal/transverse stria ratio, and length and width overlapped. Sterrenburg (1995) concluded that there are no qualitative or ecological differences between the two taxa. Gyrosigma spenceri should now be considered a later subjective synonym to G. acuminatum (Sterrenburg and Underwood, 1997).


Gyrosigma acuminatum was collected in several different habitats within Dickinson County, Iowa; 1) on a windy day using a plankton net (25 µm) off a dock in Lazy Lagoon, 2) on a partially submerged branch floating in Beck’s Canal, 3) using a plankton net (10 µm) off the east side of the Harpen St. bridge, and 4) in a pool of standing water in Excelsior Fen (part of the Silver Lake Fen State Preserve).

Frustules of Gyrosigma acuminatum are large and distinct. It is primarily an epipelic species which lives unattached on fine substrates. This species is considered to be globally distributed in freshwater, but has also been observed in brackish habitats. In a study on temperature-size relationships, larger specimens of G. acuminatum were more readily observed in exposed sites in a main lake basin rather than in protected embayments (Vanden Byllaardt and Cyr, 2011). Frustules were similar in size at warm and cold sites. In that study, frustule size appeared to be related not to water temperature, but as a function of site exposure.

Autecol 3
Credit: Michelle Chaput
Live specimen showing the chloroplasts which span the length of the frustule.
Autecol 1
Credit: Michelle Chaput
Live specimen showing the nucleus in the center of the frustule.
Autecol 2
Credit: Michelle Chaput
Live specimen in girdle view.
Autecol 4
Credit: Michelle Chaput
Live specimen in girdle view during cell division (a thin band of silica is visible along the apical axis in the center of the frustule.
Autecol 5
Credit: Michelle Chaput
Live specimen in girdle view at the beginning of cell division.

Original Description

G. acuminata Rabenh. (F. 5. a.) Selten über 6-7/100 Mm. lang, robust, zuge-spitzt, stumpflich. Durch ganz Europa, Bogotá.

  • Basionym
    Frustulia acuminata
  • Author
    Kütz. 1833

Original Images

Gomphonema acuminatum orig illus
G Acuminatum Orig Des

Cite This Page

Chaput, M. (2014). Gyrosigma acuminatum. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/gyrosigma_acuminatum


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