• Category
  • Length Range
    67–176 µm
  • Width Range
    23–35 µm
  • Striae in 10 µm
  • Reported As
    Surirella terryana (Hustedt 1912 in Schmidt et al. 1874-1959; pl. 280/6-8)
    Surirella sp. 1 (Siver et al. 2005; p. 210, pl. 88/5)



Valves are linear with rounded cuneate ends. Valves are typically slightly heteropolar, narrowing towards the foot pole, although some specimens appear isopolar. Valves are slightly, to distinctly, twisted along the apical axis. The valve length is much more variable than the valve width, with the valve length to width ratio ranging from 2.9 to 6.1. Valves are distinctly corrugated. The axial area is narrow and thickened to give the appearance of additional silicification in LM. Porcae are alternate to opposite, within a valve. An alar wing is evident. The raphe is placed in a raised canal and the canal appears about as wide as the fenestrae, which number 16–25 in 100 μm. Fenestrae are typically D-shaped in outline and partially occluded by 7 fenestral bars. The axial area is narrow, elevated to the level of the porcae, without ornamentation or pores. Porcae are ornamented with minute papillae and larger, short, bluntly pointed spines. The spines appear as coarse granulation in LM. Striae are mostly biseriate, sometimes triseriate, often becoming uniseriate towards the median area and radiate at the apices.


Surirella terryi was observed only in 11 freshwater lakes and small streams in coastal areas of the northeastern U.S. (CT, DE, ME, NJ, PA) and Washington state, all within 60 km of the ocean shore. It was fairly abundant in the type material (Ice Pond, New Britain, Connecticut) and Lee’s Pond in Bristol (ca. 15 km west of New Britain), where hundreds of valves of S. terryi were present. In all other slides S. terryi was present in much smaller numbers (n ≤ 44 valves). An additional record of the taxon is given in Siver et al. (2005) as Surirella sp. 1. They found the species in two ponds on the Cape Cod peninsula in Massachusetts and reported it as being rare.

Acadia Np 058 1  Sur Ter1A  Inic Cell Publ
Credit: Cromwell Brook, Acadia National Park, ME.
Initial cell

Original Description

In five different ponds in Bristol I have found an abundance of a new Surirella, and in one of these ponds it is the predominating form. It is about the size of S. gracilis A. Schm., but not so alate, and with rounded ends, costa distinct, reaching the median line, which is strongly marked; most specimens have a slight spiral twist. It occurs in two types, one greatly elongated. The living frustules are sometimes covered with coarse granulations that do not come off in the acid treatment, but are removed by the soda. Prof. H. L. Smith wrote me "This Surirella is certainly new and much more deserving of a specific name than many others." Dr. Ward named it Surirella Terryi. I have found this species abundant in one small pond in New Britain and in one at Leete’s Island, but in all other localities known to me it is extremely rare.

  • Author
    Ward ex Terry 1907

Original Images

Terry1907  Sur Terryi Description

Cite This Page

Veselá, J. (2012). Surirella terryi. In Diatoms of North America. Retrieved May 18, 2024, from https://diatoms.org/species/surirella_terryi


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