As with other ptyctodonts, the armor of Ctenurella was reduced to a few thin plates on the head and shoulder region. It was also relatively small for a placoderm, at just 13 centimetres (5 in) in length. It had two dorsal fins, with that at the rear of the body being relatively long and low, and large pectoral and pelvic fins. Most ptyctodonts are presumed to have fed on the ocean floor, but the well-developed fins of this genus indicate that it probably also swam in open waters.
Ctenurella had a long, whip-like tail, large eyes, and robust upper and lower jaw tooth plates. Males also had hook-shaped sex organs, known as claspers. Since analogous features are also found in the unrelated living chimaeras, chimaeras and ptyctodonts are thought to be an example of convergent evolution.
The specific name of the type species, C. gladbachensis, is a reference of the place Bergisch Gladbach, where it was founded.