In the deep ghoul star sector, a splinter of hive fleet leviathan presses in from the stars gently drift into the heavy mists and gases of Absimilard 7, a gas planet that was long since abandoned by the savage aliens of that star system.
Many of the Leviathan bio-starships opened their several hooked maws and limbs while several reconnaissance and interceptor organism flocked out such as gargoyles and harpies. Some of them descended past the massive storm layer and found themselves with a realm of raging winds, rains and spiraling seas. Below this great gas giant was a massive oceanic world with clouds at times as dark as night. The smaller organisms instantly died, torn to shreds by the whipping winds be even as the where sucked into the planets gravity core they gave a vision of the tidal underworld of watery life. The massive organic star ships grew hungry, they lowered themselves within the churning layer of thick methane, nitrogen and oxygen clouds, many of their breathing vents easily opened up to begin filtering these gases within their bodies and in turn create carbohydrates, lipids and proteins from photosynthesis. When in need of water they easily lowered themselves into the oceanic churning saline waters and use their massive probisci to siphon the ancient planets antediluvian seas. They would then raise themselves high above the cloud layer to the very highest stratosphere of the planet and let the unlimited numbers of algae and plankton with their hides synthesize their needed building blocks of life. Eventually these ships would begin to bread by releasing millions of spores within the wind from their angiosperms, this would turn fall into the gynoducts of other organic leviathans and begin to germinate. The germination would begin to form into pods filled with algae, bacteria, extremophiles, simple worms and viruses and fall to the ocean's water below. The heavens themselves where cleared of the massive clouds of brownish methane and ash while the waters where propagated with life. The seas after a few hundred years would be massive pools of nutria that would bear the countless starships and warrior organisms for the fleet, but in this stage they would need to learn to hunt, fight, devour, hide and breed in this watery world. In less that two hundred years the oceans turned green with algae and the skys where sucked clear from the primordial gases, the psionic forces of the various leviathans slowly pulled the gas giant closer to the star it was orbiting. In time they would be able to pull the planet within the warp or through the very void of space but for now they where content to breed and grow into a massive fleet, slowly devouring or commandeering every gas giant within this small sector and regenerating their once massive fleet.
Soon some of the lesser organism began to slowly fall into the sea system, The Hiveships watched with their massive psychic scrying powers. The heavy waters churned and sucked up the warrior organisms, some of them perished such as the but in time each generation was adapted to deal with it's environment. Those that perished simply feed the thriving ocean lifecycle and those that adapted quickly evolved into apex predators of their aquatic environments. Termagaunts and Hormigaunts legs quickly developed chitin paddles and their appearance was changed to be more shrimp like, they swiftly darted from stone to stone catching lesser invetebrates like crabs and squid within their maws. Carnifex, maleceptors, toxicrenes did not change much and became like massive scavenger crabs below the sea, devouring carcasses of aquatic termagaunts that died from birth or mating battle. Lictors and Genestealers bones changed to be like cartilage and they became stealthy predators similar to octopus and cuttle fish, changing colors and striking when the time was right. Tyrgons and Mawlocs became like giant whales that either hid in the mud to ambush foes or swam and devoured thousands of prey within an instant. Other tyranids like zoanthropes slept within the Hiveships or levitated below, stayed invisible and acted as the eyes and the ears of the evolutionary changes and growths of the tyranid creatures. The Hive sheeps began to descend within 1000 years, slowly devouring their virile progency and then using their gathered biomass to bud into new star ships or merge dna to form larger and more psionically powerful starships.