Balloon Mycostrum
Balloon mycostrums evolved as silk mycostrums (alongside their silk knightworm symbiotes) left their mountains and moved into the wooded parts of northern Barlowe. Their lifestyle stayed the same in most regards, but they developed a radical new form of dispersal. No longer able to disperse from mountaintop to mountaintop by shooting strands across chasms, they instead took to the air. Shooting strands into the air often, by luck, caught the wind and blew a mycostrum far away. Balloon mycostrums capitalized on that by developing a new form for ballooning.
In this form, their fibers condense into thin, strong strands, which can reach about a meter in length. Several of these strands fan out into a triangle shape, held together by lighter, fluffier strands, forming a kite to catch the wind. These can grow out of any of the mycostrum fibers, but they most commonly grow out of fruiting bodies, providing a means for offspring to spread far and wide. Once detached from the main organism, this balloon catches the wind and soars away. They even managed to cross the strait between Barlowe and Hydro, thus colonizing a relatively empty landmass.
Balloon mycostrum is most often found in its nest form. This is a condensed, soft mass, perfect for balloon knightworms to rest on and to incubate their eggs in, and it retains moisture after rain, providing a medium for balloon knightworms to drink from and spawn in. Bits of mycostrum will also detach to be carried around by individual knightworms, forming an insulating layer and able to be shaped to form strands for crossing from place to place.
The symbiosis has deepened further. Balloon mycostrums take nourishment from their symbiotes. Not only do they feed off of their excess exoskeletal growth, feces, and dead or unfertilized eggs, but the knightworms now also fertilize them with harvested flora. Additionally, when their fruiting bodies shoot out long strands to form a balloon, the knightworms will notice when there is a particularly strong wind and detach the balloon from the fruiting body. Balloon mycostrums can survive without balloon knightworms, but they cannot thrive.
Balloon mycostrum is easy to distinguish from silk mycostrum by the increased amount of loose strands of fiber. This comes hand in hand with the long strands that they use for ballooning, but they grow a fringe of many similar small strands as a byproduct. Their fruiting bodies are also taller and narrower, and as the fruiting bodies get older, they start growing longer and longer strands that will eventually form the balloon.