The latter and the Rondeletiidae are the only known living fishes which have the mysterious Tominaga's organ.

The better-known Rondeletia loricata is known from all oceans between 47°N–47°S; it has been recorded to reach a length of more than 9 cm when adult.

[1] Usually found in deep waters of tropical and temperate oceans around the world, down to 3,000 m or more, they make migrations up to shallower waters (around 100 m) at night to feed on crustaceans and amphipods.

The larvae occur in the surface waters, down to 50 m; previous to the onset of metamorphosis, they can be found in the uppermost few meters, descending as they mature.

Notochord flexion occurs at around 4 mm standard length in R. loricata.