Guide to Aulacoseira subarctica

Valves are 3-14 µm in diameter, with a mantle height of 2.5-14 µm. The ratio of the mantle height to valve diameter is equal or greater than 1. The mantle has straight sides and the valve face is flat. Rows of pervalvar areolae are curved to the right (dextrorse). there are 15-22 rows in 10 µm. The spines are robust, pointed and originate from two or three pervalvar costae. Unlike most other Aulacoseira species, A. subarctica does not have differentiated linking and separation valves; all valves have the spines of the same type. The ringleiste is solid, shelf-like.