Sternoptyx diaphana, the diaphanous hatchetfish, is a species of deep sea ray-finned fish in the family Sternoptychidae.

It is the type species of the genus Sternoptyx, and was first described by the French naturalist Johann Hermann in Der Naturforscher 1781.

[3] Sternoptyx diaphana is a short, deep-bodied fish with a laterally compressed body and a maximum length of about 45 mm (1.8 in).

In front of the dorsal fin is a toothed, pear-shaped translucent plate supported by a single spine.

[4][5] Sternoptyx diaphana has a wide distribution in temperate and tropical waters of all the world's oceans, although occurring with less frequency in equatorial seas.