Guide to Aulacoseira granulata

Valves are 4-17 µm in diameter, with a mantle height of 4-20 µm. The ratio of the mantle height to valve diameter is usually greater than 0.8 but lower than 5. The mantle areolae are square. The rows of areolae on the mantle are curved to the right (dextrorse), but often are almost straight and parallel to pervalvar axis in separation valves, 8-18 rows in 10 µm. The short linking spines are located at the end of each pervalvar costa. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long, but a few, usually 1-2 spines per valve, are very long, almost equal in length to the valve mantle. The ringleiste is solid and moderately shallow. Coiled rimoportulae are usually positioned along a stria at the distance of 1-3 areolae from the collum.