Montana Field Guide

Morphological Category - Asymmetric biraphid.

Valves elliptic and slightly dorsiventral with a bit more curvature on the dorsal side. Apices capitate to subcapitate, bent slightly towards the ventral margin. Axial area narrow, located near valve midline. Central area very small and asymmetric, formed by 1–3 short striae on one or both sides. Raphe weakly lateral; proximal ends not expanded, deflected slightly towards ventral margin; distal fissures deflected dorsally. Striae slightly radiate throughout, more closely spaced towards apices.

Size Range
Length 20–32 µm. Width 6.4–8.7 µm. Striae in 10 µm 12–16 center, up to 18 apices. Areolae in 10 µm 32–35.

Useful Link:
Diatom Glossary [Diatoms of North America website]

Cymbopleura naviculiformis has somewhat larger and more dorsiventral valves, with a large rounded central area and a lateral raphe.

Cymbopleura anglica has larger valves, a lateral raphe, and a larger central area.

Cymbopleura frequens has linear-lanceolate valves, rostrate to apiculate apices and a larger length-to-width ratio. The apices of Cymblopleura frequens are not bent to the ventral side, or are bent only slightly.

Cymbopleura similiformis has more linear and more bilaterally symmetric valves and apices that are straight, not bent towards the ventral margin.

Small headwater lakes and streams.

Cool, well-oxygenated, alkaline (calcium-bicarbonate) waters with moderate conductance.

WATER CHEMISTRY
Abundance-weighted means: pH = 8.4; conductivity = 334 µS/cm; temperature = 19.2 degrees Celsius.

Generally considered to be an indicator of good water quality.