The Hycean (Hycean hycean) is non-aggressive toward players, but it is one of the most spectacular organisms on Proteus. Evolved from squid-like ancestors, it uses bacterial symbiotes to split seawater and convert ammonia into a carbon-nitride lifting gas, letting it drift above the water surface like a living airship.
It snatches small prey with its arms and suffocates larger catches by holding them clear of the water until their gills dry. Sails let it steer with the wind. It is acutely sensitive to electromagnetic activity and shelters underwater during thunderstorms.
The catch: its gasbag is hydrogen, and highly flammable. A spark will ignite it, so never pass directly beneath one with anything that produces sparks. It may “fertilise” ocean zones with its waste, a hint at higher cognition.