• Category
  • Length Range
    17-40 µm
  • Width Range
    4.8-5.3 µm
  • Striae in 10 µm



Valves are weakly arcuate. The dorsal margin is more strongly curved than the ventral margin. In larger specimens, a weakly gibbous shoulder can be observed on the dorsal margins near the apices. Apices are subcapitate, slightly recurved dorsally and narrow (2.0-2.5 µm) . Striae are nearly parallel and are interrupted by a hyaline line near the ventral margin. The striae are separated by externally thickened, transapical costae. The costae terminate on the dorsal margin as prominent, planar wing- or spine-like projections. A reduced raphe is present on the ventral mantle interface at the apices, but it can be difficult to discern in LM. Areolae are not resolvable in LM. Rimoportulae are absent.


Semiorbis catillifera was described from epiphytic and epipsammic habitats in a shallow, slightly acidic stream in western Florida (Morrow et al. 1981). The images shown here are of the holotype slide.

Original Description

Frustule in ventral girdle view rectangular, in dorsal view sometimes broader in middle than on ends. Dorsal valve margin strongly convex, ventral margin slightly concave. Ends of valve rostrate-capitate. Terminal nodules above ventral margin near valve apices. Striae parallel, alternating with plates which obscure them. Plates fin-like, diminishing in size toward valve ends. Raphe partly on ventral valve mantle and partly on valve face. Striae 11-14 in 10 µm. Length 10-42 µm. Breadth 2.8-6.1 µm.

  • Basionym
    Eunotia catillifera
  • Author
    Morrow 1981
  • Length Range
    10-42 µm
  • Width
    2.8-6.1 µm
  • Striae in 10µm

Original Images

Eunotia catillifera orig illus
Eucatillifera Original Description

Cite This Page

Burge, D., Edlund, M. (2016). Semiorbis catillifera. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/semiorbis_catillifera


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