Old wife

The old wife was originally classified in the genus Chaetodon (with the typical butterflyfishes), but it is now classified as the sole modern species of its own family Enoplosidae and genus Enoplosus. Some fossils have also been added to the genus.

The first description of the species, one of the earliest for any Australian fish, was in 1790 by John White in his Journal of a Voyage to New South Wales though some sources give George Shaw (who assisted White in the preparation of his manuscript) as the species authority. White originally named it the long-spined chaetodon (Chætodon armatus) and described it as follows:

Whitish Chaetodon, with seven black stripes on the body. Six spines on the dorsal fin, the third very long. This appears to be a new and very elegant species of the genus Chaetodon. The total length of the specimen was not more than four inches. The colour a silvery white, darker, and of a bluish tinge on the back; the transverse fasciae, or bands, of a deep black; the fins and tail of a pale brown. The third ray or spine of the first dorsal fin is much longer than the rest.

The species was reclassified by Lacépède into its own genus (named from "weapon" in Greek to again reflect the long spines), and was moved by Cuvier from Chaetodontidae into its own separate family within Percoidei.

In 1836, Agassiz identified closely related fossils at Monte Bolca (an important fossil site in Europe) as Enoplosus pygopterus (named for its smaller fins). These exceptionally well-preserved fossils had a very similar body plan, and even a similar zebra pattern of colouring. However, more recent studies have recovered this species as actually being an early cardinalfish, moved to its own genus, Eosphaeramia.