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Zeppelins are the largest animals on Ilion, though most of their body is empty space. Zeppelins are made up several individuals linked together. There are only three species.
Ghost zeppelin – These predators are built for swallowing and not much else. Killing, chewing, and digestion (not necessarily in that order) are handled by a variety of symbionts that live inside the main chamber. These include pinhole fish, annulids, lancers, plankton, and microbes. Some of these are obligate mutualists that exist only inside zeppelins. Ghost zeppelins mix their gut fauna while mating and innoculate their larval offspring with eggs, spores, and microbes before release into the open water. Facultative mutualists and commensals are acquired later in the diet.
Red zeppelin – The red zeppelin is part filter feeder, part photosynthesizer. Red algae reside on the inner body wall as a biofilm, providing the host with energy in exchange for a substrate to grow on. Stinging cells ward off most predators except for those specialized to hunt zeppelins, such as the gulf whallabeast.
Rosyhose – The rosyhose is small and elongate relative to its sister, but it lives a similar lifestyle in shallow waters. Its sting can stun most predators but it falls easy prey to razor reefs.
At first, mission scientists mourned the loss of submersible S18. It had been swallowed by an ocean dweller of massive proportions. Pale and blimplike in form, the so-called ghost zeppelin could have swallowed a humpback whale if given the opportunity. S18’s AI was not sophisticated enough to navigate the convoluted intestine of such a large animal.
Luckily for S18, the ghost zeppelin’s mouth did not lead to a digestive tract. The animal was hollow – and filled with life. Pirhana-like pinhole fish feasted upon the prey of their host. Needleworms embedded themselves in the scraps and converted the meat to a liquid form that the worms, and the zeppelin, could ingest. Plankton clouded the water and provided further nourishment for the great swallower. Only one entity remained whole once eaten, and that was the submersible itself. The S18 team hopes that the submersible chooses to explore the living cavern before finding its way out.