Ponyfishes are small and laterally compressed in shape, with a bland, silvery colouration.

They are distinguished by highly extensible mouths, and the presence of a mechanism for locking the spines in the dorsal and anal fins.

[8] Two of the most widely studied uses for luminescence in ponyfish are camouflage by ventral counterillumination[9][10] and species-specific sexual dimorphism.

[6][7][11][12] The light organ systems of ponyfishes are highly variable across species and often between sexes.

[11][12] Leiognathidae is classified within the suborder Percoidei by the 5th edition of Fishes of the World, but they are placed in an unnamed clade which sits outside the superfamily Percoidea.