Acanthoceras zachariasii

Frustules are lightly silicified and typically lie in girdle view. The pervalvar axis is long, 54-121 µm. Valves have bipolar symmetry and are characterized by two long, horn-like extensions (55-65 µm) on each valve. The girdle bands are open, with each end aligned to form a zig-zag suture. The girdle band density is 2.4-3.3 in 10 µm. Cells produce heavily silicified endogenous resting spores, which may be present within frustules. More often, the resting spores are detected in lake sediment deposits. Resting spores range in length from 14.3-41.0 µm and 5.2-11.5 µm in pervalvar axis. They have a scalloped and convex primary valve and a smooth concave secondary valve (Edlund and Stoermer 1993). Because frustules are so lightly silicified, they are often destroyed by typical processing methods. Cells are best observed by making "burn mounts".