Valves are rhombic with straight margins and rounded apices. Striae are radiate throughout valve. The central area is asymmetrically rounded and axial area is narrow and straight. Striae at the center valve margin are short, and not interrupted. The raphe is positioned within two longitudinal ribs on the external valve face. The ribs terminate at the edge of the central area and the apices. Raphe is straight and filiform. The proximal fissures are undifferentiated and the distal fissures are T-shaped. Areolae are variable in shape, mostly elongate with respect to the transapical axis. The orientation and irregular size of the areolae creates a series of wavy hyaline areas. Small papillae (visible in SEM) may be positioned on rows between the striae. A thickened rib is present along the valve margin and apex, separating the valve face from the mantle. Striae on the mantle are uniseriate and aligned with striae on the valve face.

In SEM, the internal proximal raphe fissures terminate at a small helictoglossa. Areolae are covered internally with flat, well-defined hymenes. Externally, a well-defined, thick rib defines the valve face / mantle interface. The mantle contains a single row of elongated pores, each of which is covered internally by a hymen.


Little is known about the ecology of B. hannae, since it is rarely reported. The lmited records are from acidic, humic strained waters.

Original Description

Valves rhombic; ends obtusely rounded. Axial area narrow. Central area somewhat angular. Raphe straight filiform. Striae radiate throughout, occasionally the last three or four striae at the ends may be parallel. A few short striae may be interposed between the longer striae on either side of the central area. Striae punctate. Length 25-73 µm; width 13-21 µm; striae 21-22/10 µm

  • Basionym
    Anomoeoneis follis var. hannae
  • Author
    Reimer 1966
  • Length Range
    25-73 µm
  • Width
    13-21 µm
  • Striae in 10µm

Original Images

 Anomoeoneis follis var. hannae orig illus
Anomoeoneis follis var. hannae orig descr
Original text and images reproduced with permission by Academy of Natural Sciences of Philadelphia.

Cite This Page

Hamilton, P. (2010). Brachysira hannae. In Diatoms of North America. Retrieved July 22, 2018, from


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