Ctenoplectus williamsi was an unusual early pufferfish relative whose nearly complete skeleton reveals a mosaic of primitive and specialised tetraodontiform features. It had fused tooth-bearing jaw bones and enlarged dorsal-fin supports, but retained structures lost or highly modified in many later pufferfishes. This combination makes it particularly important for understanding the rapid anatomical experimentation near the origin of modern tetraodontiform groups.

The fused jaws and anterior dental swelling indicate a strong biting apparatus, although the exact diet is unknown. Its broad plate-like dorsal spines and expanded fin radials also show substantial specialisation of the dorsal fin. Unlike many London Clay fishes known only from skulls or otoliths, Ctenoplectus preserves enough of the body to reveal how several anatomical systems were assembled in one fish.