Appearance
It has a deep and compressed body and concave forehead. These features are characteristic of typical butterflyfishes. However, the old wife is easily distinguished by its silver-and-black, vertical, zebra-striped coloration, and by its two prominent dorsal fins. The second dorsal fin is very long and sickle-shaped. The fish grows up to 50 cm long.
Its dorsal fins have bony, knife-like spines. These have no obvious venom groove nor gland. Nonetheless, the spines are widely considered to inflict a painful venom.