of marine fish. These forms are not larvae; Gnathiidae instead become parasitic during the manca stage. Mancae of the Gnathiidae closely resemble the adult form, however they lack the final pair of pereiopods.

Taxonomy in the family relies on male characters, such that females and juveniles cannot be reliably identified. The family contains 182 species, divided among the following genera:
*Afrignathia Hadfield & Smit, 2008