Platysomus (from, 'broad' and 'body') is an extinct genus of ray-finned fish that lived in the Carboniferous and Permian periods. Fossils have been found worldwide. Platysomus was about 18 cm long, and shaped similarly to the discus fish, having the same flattened body and elongated dorsal and anal fins. Its jaws were placed vertically under the braincase, giving it a wide gape. Platysomus is thought to have fed on plankton, and lived in both fresh and salt water.