Montana Field Guide

Morphological Category – Symmetric biraphid

Valves linear, subtly triundulate with a distinctly tumid middle and broadly rounded, somewhat wedge-shaped apices. Raphe branches weakly lateral. Proximal raphe ends straight or deflected slightly to the secondary side. Distal raphe fissures hooked to the secondary side. Axial Area very narrow and linear. Central Area elliptical and asymmetric, bordered by 2–5 irregularly shortened and often faint striae. Striae radiate, becoming convergent at the ends. Areolae in the striae about 30 in 10 µm.

Size Range
Length 64–76 µm. Width 6.8–8.0 µm. Striae in 10 µm 11–13.

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

Valves of Navicula angusta lack the tumid center and are more boat-shaped and less linear in appearance. Navicula oblonga is larger and more robust than N. piercei.

Mountain lakes.

Cold, circumneutral waters with very low conductivity and nutrients.

Water Chemistry
At the type locality, pH measured 7.5 and conductivity measured 40 µS/cm

Diatoms typically reproduce by cell division (mitosis) and occasionally by meiosis—sexual reproduction in which female and male gametes combine to form a specialized zygote called an auxospore. Repeated divisions result in cells of a population becoming progressively smaller and smaller. When cells reach a critically small size, sexual reproduction is initiated, resulting in an auxospore and initial cells that are the largest attainable for the species, after which cell division and size reduction resume (Amato 2010).

Climate change and regional warming, nutrient pollution.