• Category
  • Length Range
    36-65 µm
  • Width Range
    8.0-9.3 µm
  • Striae in 10 µm



Valves have smoothly arched margins, with a slight inflation at mid-valve. Valves at the lower end of the size range are slightly convex on the dorsal side. Apices are bluntly rounded, and positioned toward the ventral side. The axial area is narrow, and parallel to the raphe. The proximal raphe ends are positioned near the ventral margin. The raphe is oblique and runs from near the ventral margin to around the dorsal side passing onto the dorsal mantle. The external proximal raphe ends are slightly deflected to the ventral side. The raphe appears to be simple and straight.

The striae are uniseriate and composed of round areolae. On the dorsal side of the raphe, the striae are nearly parallel to radiate. On the ventral side of the raphe, the striae are scattered and disorganized near the central nodule. Striae are slightly divergent and may be curved. The Voigt discontinuity is distinctly marked by up to several branching striae. Distal to the Voigt discontinuity, the striae are divergent. The fascia extends through the central nodule to at least over the dorsal margin, perhaps further. The fascia is distinctly rectangular and thickened. The fascia is absent on the ventral side.

This taxon clearly belongs to a distinct group of species that should be considered as a new genus, not within Amphora. Members of this group are found in Lake Baikal, Siberia; Japan; Miocene fossil deposits of eastern Europe (Levkov et al. 2009).


Amphora delphinea var. minor was first observed in Crane Pond outside of Groveland, Massachusetts (Cleve 1895). Previously thought to be extinct, this taxon seems to be exceedingly rare, as it was not observed again until 2017 in Crosby Pond (ME), Mud Pond (NY), and in Little Watchic Pond (ME) by the National Lakes Assessment. We observed this taxon in small lakes in forested catchments, in acidic and mesotrophic-oligotrophic conditions.

Water conditions of the ponds in which A. delphinea var. minor was observed were characterized as:

Productivity: less than or equal to 7 µg/L Chlorophyll-a (mesotrophic-oligotrophic)

Dissolved Oxygen: greater than 4 mg/L

Alkalinity: less than 12.5 mg/L as CaCO

The original description of this taxon was was also reported in the Demerara River, Guyana (Cleve 1845), a large, sediment-laden tropical river. The Demerara River and Crane Pond were collected by early researchers. These sites contain odd disjunct taxa (Mann 1924) which need further investigation.

Original Description

Var. minor Cl. - V. in L. 0,06; B. 0,012 mm. Striae 24 in 0,01 mm. - A.S. Atl. XL f. 25.
Fresh water: North America, Crane Pond! Demerara River!

  • Author
    Cleve 1895
  • Length Range
    60 µm
  • Width
    12 µm
  • Striae in 10µm

Original Images

Amphora delphinea minor orig illus
Amphora delphinea minor orig desc

Cite This Page

Ellertson, C. (2021). Amphora delphinea var. minor. In Diatoms of North America. Retrieved July 15, 2024, from https://diatoms.org/species/amphora-delphinea-minor


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Amphora delphinea var. minor 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.