Valves are strongly arched, with rostrate ends. Specimens at the large end of the size range have a dorsal inflation near the apices. External, conspicuous transapical costae are present. The transapical costae terminate into short flat spines at the valve face-mantle junction. Striae occur between the transapical costae, composed of uniseriate areolae (not visible in LM). A reduced raphe is present on the ventral valve mantle interface at the apices (may not be discernable in LM). Rimoportulae are absent.
This taxon has been documented from a small, shallow lagoon on Outer Island, in the Apostle Islands National Lakeshore, Wisconsin. Edlund et al. (2021), however, suggest several other studies show specimens (Camburn and Charles 2000) that will, upon closer examination, expand the range of this taxon. These sites are also low conductivity, slightly acidic to circumneutral habitats.
Living cells were commonly observed, in which cells were joined along the ventral apex into a spherical colony.
Cells lunate with dorsal sides slightly broader compared to ventral sides, lanceolate in girdle view (Figs 29–36). Cells arranged in colonies constructed of four to many cells adjoined at their valve ends in circular groups with their dorsal mantles and cingula facing outward. Cells with a centrally located nucleus and two plate-like valve-appressed chloroplasts in each cell. Storage bodies common and likely polyphosphate (libroplasts) or chrysolaminarin (Figs 48–50). Valves lunate with somewhat broader dorsal mantles (Fig. 53), slightly rostrate ends, parallel margins that may be slightly constricted mid-valve in smaller specimens, and conspicuous external transapical costae (Figs 29–36). Valve length 16.5–40.5 µm, breadth 3.6–5.7 µm, stria or transapical costa density 8–12 per 10 µm, and dorsal curvature from 0.05 to 0.12. In scanning electron microscopy, transapical costae terminating dorsally and ventrally in short, flat spines at the facemantle junction. Costae continuing onto the valve mantle (Figs 51–53). A short raphe slit present at each valve end, externally starting on the ventral mantle and curving onto the valve face at each end (Fig. 52), internally limited to the ventral mantle and terminating in a small helictoglossa (Figs 54–55, 57). No rimoportulae present (Figs 55, 57). One stria between neighbouring costae (Fig. 53), striae uniseriate, sometimes becoming biseriate toward the face-mantle junction, and continuing onto the valve mantle (Figs 53, 56). Areolae without external occlusion, internally occluded by a hymen (Fig. 56). Cingulum of 3–4 split bands, each with a single row of areolae (Figs 52–53).
Burge, D., Edlund, M., Stone, J. (2021). Semiorbis eliasiae. In Diatoms of North America. Retrieved April 18, 2024, from https://diatoms.org/species/semiorbis-eliasiae
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Semiorbis eliasiae 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.