Montana Field Guide

Morphological Category – Symmetric biraphid

Valves linear and triundulate. Undulations approximately equal in width, or middle undulation slightly wider. A longitudinal line runs along each side of the valve. Apices broadly rostrate. Axial Area narrow, barely wider than the raphe. Central Area elliptic and about half the width of the valve at center. Raphe filiform, proximal ends straight, not bent and only slightly expanded. Striae moderately radiate at the center, becoming parallel then weakly convergent at the apices. Areolae in the striae distinct, 20-24 in 10 µm.

Size Range
Length 27-47 µm. Width 6.6-8.9 µm. Striae in 10 µm 21-24.

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

Neidiopsis hamiltonii has lanceolate valves with smooth (not triundulate) margins. Neidiopsis wulffii has linear-elliptic valves with short, protracted apices and proximal raphe ends deflected to the same side. Valves of Neidiopsis weilandii have smooth, weakly convex to nearly parallel margins and proximal raphe ends bent to the same side. In Neidium species, proximal raphe ends are hooked towards opposite sides of the valve.

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).