Moythomasia is an extinct genus of early ray-finned fish from the Devonian period of Europe and Australia. Moythomasia was a small freshwater fish, 9 centimetres (3.5 in) long. It had relatively large eyes, presumably to find prey in murky water. Its body was covered in specialized ganoid scales; the upper side of each scale sported a small pin that perfectly fit into the hollow lower side of the next scale. This allowed the fish to be both armored and flexible.