Moythomasia (named for James Alan Moy-Thomas) is an extinct genus of early ray-finned fish from the Devonian period, known from fossils found in Europe and Australia.
Moythomasia was a small freshwater fish, measuring about in length. It had relatively large eyes, likely to help it locate prey in murky water. Its body was covered in specialized ganoid scales; the upper side of each scale featured a small pin that perfectly fit into a hollow on the lower side of the adjacent scale. This unique structure provided both armor and flexibility.