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.