The notchheaded marblefish was first formally described in 1889 as Haplodactylus etheridgii by the Northern Ireland born Australian herpetologist and ichthyologist James Douglas Ogilby with the type locality given as the Admiralty Islets off Lord Howe Island.

[2] The specific name of this fish honours the British geologist and paleontologist Robert Etheridge Jr., the leader of the expedition on which the type was collected.

[3] The notchheaded marblefish has an elongate body which has a depth equivalent to roughly a quarter of its standard length.

The dorsal fin has a long base but it is nearly split in two by a deep and wide incision between the spiny and soft rayed parts.

The body is covered in small, cycloid scales which are embedded in the skin, these extend on to the cheeks and operculum and create a sheath along base of the spiny portion of the dorsal fin.