The order consists of about 33 species in six extant families, mostly deep-sea types.

Uniquely, despite its age, Cretazeus is thought to be a derived crown-group zeiform closely related to the Parazenidae (in contrast, the two most basal zeiform families are known from later, during the early Paleogene).

This suggests that at least six lineages of zeiforms were present during the Late Cretaceous and survived the Cretaceous-Paleogene extinction, despite this not being preserved in the fossil record.

[3][4][5][6] Aside from Cretazeus, an earlier record of the zeiforms is an indeterminate fossil otolith ("genus Zeiformomum" tyleri) from the Santonian of Spain, but its specific affinities remain uncertain.

[3][7] A potentially older genus, Palaeocyttus of Portugal, is known only from a poorly-preserved specimen and may not be a zeiform.