Aulacoseira alpigena

Frustules are cylindrical and 4-15 µm in diameter, with a mantle height of 4-7 µm. The ratio of the mantle height to valve diameter is less than 1. The mantle has convex sides and the valve face is flat. Rows of pervalvar areolae are curved to the right (dextrorse) and number 15-22 in 10 µm. The valve face is unornamented except for one row of marginal areolae. Spines are located at the end of each pervalvar costa. Spines are thin and have an 'anchor' shape at the end. The ringleiste is small.

Some valves of A. alpigena have almost straight rows of mantle areolae that also may be almost parallel to the pervalvar axis. Such specimens have been often misidentified as A. distans (Ehrenberg) Simonsen. Crawford and Likhoshway (1999) examined the type material of A. distans and showed that it is characterized by numerous rimportulae that internally form short tubes, situated close to a very deep ringleiste. These rimportulae are easily observed in LM in valve views. A. alpigena does not have such prominent and numerous rimoportulae and differs from A. distans also by having higher density of mantle areolae, shallow ringleiste, and plain valve face.