Plectorhinchus chaetodonoides has fleshy lips which become moderately swollen as the fish grows, there are 6 pores on the chin but no central pit. The dorsal fin typically has 12 spines, although rarely it has 11 spines. and 18-20 soft rays, the soft rayed part of the dorsal fin has a height which is roughly equal to the length of its base. The juveniles are brownish with large, discrete creamy white blotches on the body these develop brown spotting as the fish matures. As they grow into adults the coloration slowly develops a greyish background colour broken large, dark brown spots, these spots having a greater diameter of the iris. The maximum recorded total length is 72 cm (28 in), although 60 cm (24 in) is more typical, and the maximum published weight is 7 kg (15 lb). It is thought that the juveniles are Batesian mimics of poisonous flatworms. The caudal fin of juveniles is deeply forked and has wide rounded lobes both of which are mostly white marked with a large brown spot, in adults it is much less forked.
