Montana Field Guide

Morphological Category – Asymmetric biraphid

Valves lanceolate-clavate; headpole rounded and slightly protracted; footpole narrow, rounded. Valve tapers gently towards the headpole, more strongly towards the footpole, especially in shorter specimens. Raphe undulate and lateral. Axial Area narrow at the poles, straight, widens at the center to form a small, somewhat rounded central area. A single round stigma in the central area. Striae radiate throughout. Longitudinal lines close to axial area; indistinct in some specimens. Apical pore field small.

Size Range
Length 34–90 µm. Width 11–15 µm. Striae in 10 µm 11–12 at valve center; 14–16 at the apices. Stigmata 1.

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

Valve shape and larger size distinguish G. septa from G. eriensis var. variabilis. Gomphadelpha montana is smaller and more gracile than G. septa.

Lakes, rivers and creeks.

Cold, circumneutral waters with low conductivity and nutrients.

Water Chemistry
Conductivity = 539 µS/cm; pH = 8.3; water temperature = 5.6 degrees C; total nitrogen = 0.290 mg/L; total phosphorus = 0.023 mg/L.

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.