• Category
  • Length Range
    49.9-138.6 µm
  • Width Range
    22-31.7 µm
  • Striae in 10 µm
  • Synonyms
    Navicula amphigomphus Ehrenb.
    Neidium iridis var. amphigomphus (Ehrenb.) O'Meara



Valves are large and linear to linear-elliptic, with cuneate apices. The valve face is flat. Valve margins are nearly parallel to slightly convex. Multiple longitudinal canals (3-5) are present along the valve margin. The axial area is straight to slightly expanded. In the largest specimens, the axial area may bear irregular markings on both sides of the raphe, while the axial area tends to be hyaline in small to medium sized specimens. The raphe is mostly oblique, becoming thread-like near the terminal end. Proximal raphe ends are small and strongly hooked in opposite directions. Distal raphe ends form lacinia, although this feature is difficult to resolve in LM. Internally, valves bear a rectelevatum. Helictoglossae are small, but can be resolved in focal deep planes.

The striae are slightly oblique across most of the valve face, but the angle of the striae differs bilaterally at the apices, with striae becoming parallel on opposite sides of the raphe at each apex. The central area is elliptic and slightly elongate along transapical axis. Voigt’s discontinuities, when present, are subtle. Areolae are relatively small and round near the axial area, becoming large and transapically elongate near the valve margin.

The smallest specimen presented here is shorter than the minimum length provided for this taxon other publications (Siver and Hamilton 2011, Lefebvre and Hamilton 2015). The maximum length observed in this population is roughly the same as the maximum length reported (Lefebvre and Hamilton 2015) in modern populations, but those authors also reported specimens up to 167 µm long and 42 µm wide in Ehrenberg's type material.

In SEM it can be resolved that areolae are open externally and internally are occluded by a hymen (Siver and Hamilton 2011). Renilimbia are located near areolae across the valve face (Lefebvre and Hamilton, 2015). The valve walls are chambered both apically and transapically (Lefebvre and Hamilton, 2015), similar to N. rudimentarum, N. ampliatum, N. gracile, N. hitchcockii, and N. tumescens (Hamilton et al. 2004).

Although the unique morphological features of this taxon have helped reduce the number of misidentifications compared to other large Neidium taxa such as N. iridis, some errors can be found in older literature. The specimens presented in Krammer and Lange-Bertalot (1986), for example, do not fit within the current morphological species concept (Lefebvre and Hamilton 2015).


This taxon has been reported from lake, pond, and wetland habitats, from sites in Ontario and New York (Lefebvre and Hamilton 2015), England (Patrick and Reimer 1966). The specimens illustrated here were collected from a marsh near Brainard Lake and Lake Clayton in the Indian Peaks Wilderness of Colorado. This taxon often co-occurs with Pinnularia.

N. amphigomphus helictoglossa
N. amphigomphus helictoglossa is readily viewed by optical dissection under LM.
N. amphigomphus rectelevatum
N. amphigomphus has a rectelevatum clearly visible under LM.
N. amphigomphus under LM
Cleaned N. amphigomphus specimen with its distinct yellow appearance under LM.
Home of N. amphigomphus
Credit: Lane Allen
Brainard Lake marsh, Colorado, July 2021

Original Description

133 N. Amphigomphus, testula major oblonga, lateribus a dorso planis apicibus argute cuneatis, lineis longitud. obsoletis insignis. Icon!

  • Basionym
    Navicula amphigomphus
  • Author
    Ehrenb. 1843
  • Length Range
    106–167 µm
  • Width
    26–42 µm
  • Striae in 10µm

Original Images

Neidium amphigomphus orig illus
Navicula amphigomphus orig desc

Citations & Links



Cite This Page

Araujo, C., Allen, L. (2022). Neidium amphigomphus. In Diatoms of North America. Retrieved May 25, 2024, from https://diatoms.org/species/neidium-amphigomphus


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