This taxon has a slightly sigmoid, linear valve which gradually tapers to obtusely rounded symmetrical ends. The ends sometimes appear scalpelliform. The axial area and the raphe are sigmoid or slightly undulate. The proximal raphe ends curve in opposite directions and are distant. There is a large terminal end that is eccentric and lateral. The central area is oblique. The transverse striae are more distinct that the longitudinal straie with the exception of along the axial area. The longitudinal striae are more distinct there because of the arch of the valve. The longitudianl straie are finer than the transverse striae and they cruve outward to the sides of the central area(Patrick and Reimer 1966).
Synonyms
Pleurosigma nodiferum Grun. in Cl. & Grun., K. Svenska Vet.-Akad. Handl., Ny Foljd, 17(2):59. 1880(Patrick and Reimer 1966).
Gyrosigma spencerii var nodifera (Grun.) Cl., K. Svenska Vet.-Akad. Handl., Ny Foljd, 26(2):117. 1894(Patrick and Reimer 1966).
Ecology
This taxon prefers fresh to slightly brackish water(Patrick and Reimer 1966).
Length is 60 to 150 micrometers (Patrick and Reimer 1966).
Width is 11 to 14 micrometers (Patrick and Reimer 1966).
Transverse striae are 17 to 20 in 10 micrometers (Patrick and Reimer 1966).
Longitudinal striae are 22 to 24 in 10 micrometers (Patrick and Reimer 1966).