Flattened, oval body, its height being up to 45% of its length. Second ray of dorsal fin very long, with a conspicuous dark, fringed broad membrane. First 3 or 4 dorsal fin rays generally blackish in adults but only the elongated second ray is dark in immature fish. Mottled sandy brown coloration with dark blotches on lateral line and at base of caudal fin. First rays of the dorsal fin are separated and the second one is elongated. Lateral line curves over pectoral fin.

It looks like Arnoglossus laterna (Scaldfish) which is very similar to Arnoglossus thori, but can be distinguished as it does not have dark blotches on lateral line and at base of caudal fin.