Halitrephes maasi, commonly known as the firework jellyfish, is a species of deep-sea hydrozoan of the family Halicreatidae.

Sightings have been reported at depths of 4,000 to 5,000 feet (1,200 to 1,500 m) near the Revillagigedo Archipelago off the Baja California Peninsula.

[1] Although not much is known regarding this species, H. maasi has been observed in both temperate and tropical waters of the Atlantic, Indo-Pacific, Antarctic, Mediterranean,[2] and eastern Pacific.

[3] This hydromedusa is typically bathypelagic, most commonly found in oxygen-minimal zones and deep waters.

[4] Like all cnidarians, H. maasi is a diploblastic acoelomate metazoan.