Leviathan (Grand Tour)

Leviathans, known to themselves as the Kin, are a gigantic whale-like species native to a layer of liquid water on Jupiter. They are the only extant sapient species in the Solar System aside from humans.

Anatomy & Physiology
Leviathans are vastly larger than any Earthly organism, averaging 10 kilometers (6 miles) long. They have vaguely whale-like bodies lined with flagella that look like flippers. Their upper bodies are dotted with hundreds of small eyes, and their undersides have numerous small openings that they use to feed. They also have bioluminescent organs lining their bodies.

Despite their solid appearance, leviathans are actually superorganisms, more like Portuguese man-o'-wars than whales. They are composed of several hundred smaller organisms, which are themselves gigantic by terrestrial standards.

Diet
Leviathans feed on organic "snow" that falls from Jupiter's upper atmosphere. This "snow" consists of long-chain carbon molecules that form in Jupiter's atmosphere and pieces of the organisms that live there. Leviathans are capable of killing and eating creatures almost as large as themselves, but this is rare, and leviathans generally consider it unpleasant.

Reproduction & Life Cycle
Leviathans are asexual. They reproduce by splitting into their component parts, which then divide into two. When the parts reunite, they form two leviathans instead of one. These "buddings," as the leviathans call them, occur roughly once every Jovian year (around once every 11.5 Earth years). It is unknown exactly how long leviathans live, but their lifespans are implied to be centuries or even millennia long.

Environment
Leviathans live in Jupiter's ocean, a layer of liquid water deep in the planet's atmosphere. It lies 50,000 kilometers (30,000 miles) below Jupiter's cloud tops and is 5,000 kilometers (3,000 miles) deep. There is no surface or floor; the atmosphere transitions smoothly into the water ocean, and the water ocean into a sea of liquid hydrogen below. The water contains high amounts of ammonia and sulfur, making it highly acidic. It is also under intense pressure, many thousands of times greater than at Earth's surface, and is hot enough that it would boil without such pressure.

Society and culture
Leviathans live in groups called Kin. These groups are much like whale pods, consisting of dozens to hundreds of individuals led by Elders. The Elders travel at the group's center and govern all collective actions of the Kin. The Elders are extremely conservative and hold a semi-religious reverence for the Symmetry, a term which refers both to their traditions and to the ecological balance of their environment.