Montana Field Guide

Morphological Category – Symmetric biraphid

Valves linear to elliptic, apices rostrate to subrostrate. Axial Area narrow; Central Area relatively large, circular to quadrilateral and transapically elongated. Raphe straight; proximal raphe ends slightly enlarged; distal raphe ends difficult to resolve. Partecta 5–8, all the same size. Striae uniseriate and weakly radiate, becoming nearly parallel near the apices. Areolae coarse, 20 in 10 µm.

Size Range
Length 23.8–44.8 µm. Width 7.9–10.4 µm. Striae in 10 µm: 13–15.

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

Mastogloia lacustris has larger proximal raphe ends and more radiate striae, especially surrounding the central area. Mastogloia elliptica has coarser areolae and a sinuous raphe with proximal raphe ends extending into the central area.

Cold, calcium-rich fens and pools (Bahls 2023).

Water Chemistry
At the type locality (Connelly Fen) pH = 7.42 and specific conductance = 1600 µS/cm (Bahls 2017).
At the Iowa location, pH = 6.90, conductance = 3400 µS/cm and temperature = 13.1 degrees C.

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).