Skywhale (To'ul'h species)
Image from RAP 2000
The skywhale is a large invertebrate flying filter-feeder on the planet To'ul'h Prime. It uses a reservoir of buoyant hydrogen gas to float in the dense air of this planet, and is an active, if rather slow, swimmer. The low oxygen fraction of the atmosphere reduces the likelihood of fire in these animals and related species.
Although it has no true backbone, it has a strong dorsal network of chord-like structural members that prevent the gas-bags from ripping; these chords have evolved from the same structures that have developed into the To'ul'h vertebrate backbone. The nervous system however is separate from these structural elements, and the major nerve chord is ventral in location.
The Skywhale is a member of the hyperthermophile superkingdom of To'ul'h Prime, but has evolved to live in the much cooler upper atmosphere, where it grazes on the skyplankton. Several other species of thermophiles and hyperthermophiles have adapted to the cooler upper atmosphere, where the skyplankton is abundant.
Many skywhales carry populations of photosynthetic plankton on their skin; this relationship benefits the whale indirectly, since the skyplankton supports specialised zooplankton which also protect the whale against parasites.
The Basket-mouth skywhale has dual oral palps that function as 'nets to catch plankton. Each palp is made of lightweight gas-filled tissue and has a sieve-like structure. The tail provides counterbalance and steering; this species floats passively with the air currents until it encounters a skyplankton 'forest', then gently propels itself through the mass to collect food.