Montana Field Guide

Morphological Category – Asymmetric biraphid

Valves elliptic-lanceolate with convex margins and rostrate to subrostrate apices. Valves symmetric to both apical and transapical axes. Axial Area narrow at the apices, widening gradually towards the central area. Central Area moderately large, variable in shape, most often transversely elliptic to rectangular, sometimes shaped like a bow tie. Raphe branches lateral, narrowing towards the ends. Proximal raphe ends deflected gently towards the ventral margin and terminate in slightly inflated pores. Terminal raphe fissures hook-shaped, deflected towards the dorsal margin. Areolae variable in density, 20 in 10 µm at valve center, up to 30 in 10 µm at the apices.

Size Range
Length 41-54 µm. Width 9.7-11.4 µm. Striae in 10 µm: 14 at valve center, up to 22 at the apices.

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

Distinguished from other species in this genus by its symmetric valves. Cymbopleura tynnii is much larger. Cymbopleura stauroneiformis has rhombic-lanceolate valves and narrower apices.

Calcium-rich, spring-fed fens.

Cool, alkaline waters. At the type locality, vegetation is composed almost exclusively of the Eleocharis quinqueflora community type. The fen and adjoining stream channels support large populations of three rare plant species: Primula incana, Castilleja gracillima, and Castilleja minor v. exilis. Cymbopleura laszlorum was an uncommon element (<1 % abundance) of a benthic diatom association dominated by Mastogloia lacustris, Cymbopleura florentina and Epithemia argus, in decreasing order of numerical abundance. Cymbopleura laszlorum is believed to be a glacial relic. During the Wisconsin glaciation, the adjacent mountain ranges (Madison, Tobacco Root and Gravely Ranges) were capped with ice.

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.