Valves are elliptic-lanceolate, with broad, unconstricted apices. The axial area is wide and indistinct. Striae are parallel, with individual erratic striae that intrude into the axial area. Costae are primary and robust, and become inflated and relatively indistinct in axial area; 3-4 in 10 µm. A single rimoportula is present at one valve end. Girdle bands are incomplete. Septae extend approximately 1/4 of the way into the valve, and alternate orientation from one band to the next.
Recent work suggests that the name of this taxon needs to be reconsidered (Williams et al. 2021) and this page needs to be revised. Tetracyclus rupestre may a European species.
The specimens imaged for this page were collected from Nantahala River near Rainbow Springs, North Carolina. Similar to T. hinziae and T. glans (2/4 of the other extant Tetracyclus species known) populations in the Pacific Northwest, T. rupestris is found to co-occur with specific araphid taxa in the Tabellaria, Meridion, and Odontidium genera.
Bishop, I. (2016). Tetracyclus rupestris. In Diatoms of North America. Retrieved February 28, 2025, from https://diatoms.org/species/51206/tetracyclus_rupestris