Cosmarium denticulatum var. triangulare Grönblad

Cosmarium denticulatum var. triangulare Grönblad *

( Fig. 2F, G View FIG )

Acta Societatis Scienctiarum Fennicae, Nova Series B, 2 (6): 17 ( Grönblad 1945).

DISTRIBUTION. — South America. Amazon Basin: Grönblad (1945); Förster (1969); Thomasson (1971); Cadima (2013). Western Amazonia (lowlands): no records.

DESCRIPTION

Cells 165.0-176.5 µm long, 108.0-114.5 µm wide, isthmus 35-42 µm, cells 1.5-1.6 times longer than wide. Cells with deep median constriction, median sinus narrow, closed, and dilated at the apex; cell wall punctate, denticulate at margins and above the isthmus, with central part smooth (clearly shown in Fig. 2F View FIG ). Pyramidal semicells with rounded basal angles, occasionally with one prominent denticle at each basal angle, lateral margins straight to slightly convex, converging towards apices; apical angles slightly rounded; apical margin subtruncate to broadly truncate, narrow.

REMARKS

This taxon is easily recognizable by having pyramidal semicells, with their apical margins subtruncate to truncate, and by a smooth central part area in the semicells, while the surroundings are punctate. Our specimens’ dimensions coincided with those depicted in Grönblad (1945) but are larger than the specimens described by Förster (1969).