Subterradron

The Yannickian-Bloodian extinction event was one of the most devastating events in the geologic timescale of Sagan IV. A dramatic increase in global volcanic activity triggered a near global glaciation event, and wiped the slate clean in nearly all regions of the planet. The Vivus volcanic region was no exception to this devastation, and nearly all life, save for the hardiest microbes, went extinct. And yet the cavedron, the last surviving member of an entire kingdom of life, clung on. While most all populations were indeed killed, a tiny sliver held on in the water table. As they exchange gas through cutaneous respiration, and while they could survive in an aquatic environment, they have to go through drastic changes to survive. Thus, replacing their ancestor, the subterradron has, from these humble beginnings, become an extremely successful species and a staple of the entire Dixon-Darwin-Vivus subterranean ecosystems. Much like their ancestor, they are provided nutrients by the cave rustmold in exchange for their spores being spread and thanks to their success, they have allowed the spread the cave rustmold and the clingerpede to all environments they occupy. The cave rustmold also break down the minerals in the cave walls, allowing the subterradron to use them for nutrients, in exchange for the waste products that they produce. They are able to cling to wall and ceilings because of modified tentacles that burrow into the rock, then inflate at the bottom. They wait for a clingerpede to eat them causing the bulbs to be ingested. These bulbs are now indigestible by the clingerpede, and are expelled in their waste. These contain both the subterradron embryos and spores cases for the cave rustmold.