Rusty Flathead

Inegocia japonica has 9 spines in the first dorsal fin, the first, very short spine may be detached or be connected to the second spine by a membrane. The second dorsal fin has between 11 and 13, typically 12, soft rays, as does the anal fin. It has an elongated an moderately flattened body with a large, flattened head with the supraorbital ridge being smooth to its front and serrate over the rear of the eye. The is no preorbital spine, there is a single preocular spine and the suborbital ridge is smooth apart from 2 spines under the eye. Specimens from the southern parts of the range may show a few additional small serrations on the suborbital ridge. There are typically 3 spines on the preoperculum spines with the upper spine being short not too different in size from the lower spine. There is a long flap between the eyes. The caudal fin is rounded. The overall colour ranges from orange to brown marked with flecks or mottles, with a pale belly, and with numerous variable sized dark spots on the caudal fin. The maximum published total length of this species is 35 cm (14 in), although 20 cm (7.9 in) is more typical.

Inegocia japonica has a wide Indo-West Pacific distribution. It ranges from Sri Lanka and India east to the Philippines and Papua New Guinea, north to southern Japan; south to Australia from Cockburn Sound, Western Australia to Moreton Bay, Queensland. There is a record from Réunion, the holotype of Platycephalus borboniensis, however, this appears to be erroneous. This is a demersal species found on sandy and muddy substrates in bays and coastal waters at depths between 5 and 85 m (16 and 279 ft).