Guide to Aulacoseira granulata var. angustissima

Valves are 2.5-4 µm in diameter, with a mantle height of 8-20 µm. The ratio of the mantle height to valve diameter is greater than 3.2.The rows of mantle areolae are curved to the right (dextrorse), but often are almost straight and parallel to pervalvar axis in separation valves. The rows of mantle areolae number 10-20 in 10 µm. Linking spines are located at the end of each pervalvar costa. The linking spines are short and bifurcated. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long and broadly triangular, but 1 or 2 spines per valve are very long, almost equal in length to the height of the valve mantle.