Montana Field Guide

Morphological Category – Symmetric biraphid

Valves elliptic to elliptic-lanceolate with short apiculate apices. Pseudoseptum present at each apex. Axial Area very narrow and linear. Central Stauros narrow, linear and slightly asymmetric. Raphe filiform with straight and weakly inflated proximal ends. Striae weakly radiate throughout; one to four widely spaced striae in the central area. Areolae 22-28 in 10 µm.

Size Range
Length 22-57 µm. Width 6.8-10.0 µm. Striae in 10 µm 22-28.

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

Stauroneis sagitta is frequently identified as Stauroneis livingstonii in the United States. As described, Stauroneis livingstonii has ‘slightly triundulate sides’, which our specimens lack. However, the two species are similar in all other metrics, and are here considered conspecific.

Lakes and tarns.

Cool, slightly acidic water with low nutrients and conductivity.

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.