Lactoria diaphana was first formally described as Ostracion diaphanum in 1801 by Marcus Elieser Bloch and Johann Gottlob Theaenus Schneider with no type locality given, although it is likely to be the East Indies.

[5] Lactoria diaphana has a thick, rectangular body that is largely enclosed in a carapace which is made up of thickened, hexagonal plate -like scales which are jointed to each other.

They have small mouths located at the front of the snout, with fleshy lips and a row of no more than 15 moderately sized conical teeth in each jaw.

[1] This species is the only member of the genus Lactoria with a range that extends into the southeastern Atlantic as it is found around the Cape of Good Hope and laong the southwestern coast of Africa as far north as Swakopmund, Namibia.

The juveniles are semi-transparent and are found in pelagic waters close to the surface[7] The thornback cowfish, like other boxfishes, has the ability to release a soap-like toxin called pahutoxin through their skin when stressed.