Only a handful of specimens have been observed alive, all in chance encounters with Remotely operated underwater vehicles.

[3] The largest species, the 90-cm (3-ft) long abyssal halosaur (Halosauropsis macrochir) is also one of the most deep-living fish, recorded at depths of 3,300 m (11,000 ft).

Their lateral line system enabling the detection of vibrations in the water is highly developed; the pores run the length of the fish's body.

Halosaurs are benthic fish, spending their time cruising over or resting on the sea floor, where temperatures may be just 2–4 °C.

Halosaurs are thought to prey mainly on benthic invertebrates, such as polychaete worms, echinoderms, and crustaceans such as copepods, but they may also consume small fishes and cephalopods.