• Category
  • Width Range
    7-8 µm
  • Striae in 10 µm
    10-12 in the center valve, 12-14 at the ends

Identification

Description

Valves are lanceolate-clavate and slightly asymmetric to the apical axis. The valve tapers evenly from the center to the headpole, but more markedly to the footpole. The footpole is often slightly bent. The apices of the headpole and footpole are similar in width. The axial area is narrowly lanceolate. Striae are weakly radiate at the center valve, becoming nearly parallel at the headpole and strongly radiate at the footpole. A single stigmoid is present in line with the median stria on one side of the valve. The raphe is lateral. An apical porefield is present at the footpole. Girdle bands have a single to double row of poorly arranged areolae. Length:width is 4.4 (n=17).

The specimens presented here are of the holotype population from the Escambia River, Florida. This slide was examined by Patrick and Reimer (1975) and illustrated in a line drawing. The illustration appears to have more marked tapering from the center of the valve to the headpole and more protracted apices than the specimens we observed on the holotype slide. By examining a number of specimens on the slide, we extended the size range of G. gibba previously reported by Wallace (1960, 36 μm) and Patrick and Reimer (1975, 36-39 μm).

Specimens with protracted apices at the headpole and lower length to width ratio have been reported as G. gibba. Further analysis is needed to understand the variability in valve shape and ultrastructure, as well as the distribution of this taxon.

Autecology

Gomphonema gibba was collected from Escambia River, Santa Rosa County, Florida in October 1952 by Wallace, who described the sample locality as "a typical coastal plain, meandering river, bordered by swamps" and noted the presence of a salt tongue at a depth of 7 feet at the time of collection (Wallace 1960).

Similar specimens from rivers in Georgia and Virginia could not be confirmed as Gomphonema gibba because of consistently more protracted ends and lower length:width.

Gomphonema Gibba Plate  Fl
Credit: Sylvia Lee and Mark Edlund
Gomphonema gibba specimens from the holotype slide GC 4356A observed in this study.
Gomphonema Gibba 4356 A Girdle2
Credit: Sylvia Lee and Mark Edlund
Gomphonema gibba specimen in girdle view showing pores on girdle band (holotype slide GC 4356A).

Original Description

Valvis angusti rhombeo-lanceolatis, 36 μ longis, 8 μ latis, raphe oblique. Striis medii-puncto unilaterali; central nodula distincto.

This species differs from Gomphonema ventricosum Greg. in that it lacks the orbicular central area of G. ventricosum and has instead a lanceolate axial area. The apex of G. ventricosum is broader than the base, while the apex and the base in this species are similar. In G. ventricosum the stigma is near the center of the valve and in this species the stigma approximates the end of the stria.

  • Author
    J.H.Wallace 1960
  • Length Range
    36 µm
  • Width
    8 µm

Original Images

Gomphonema Gibba  Wallace 1960
Gomphonema Gibba  Wallace 1960 Fig

Cite This Page

Lee, S, and Edlund, M. (2016). Gomphonema gibba. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/gomphonema_gibba

Responses

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