Balloon Knightworm
The balloon knightworm evolved alongside balloon mycostrum, as silk knightworms spread from Barlowe's mountains into its northern forests. The biggest changes came in their mycostrum symbiote, not the knightworm itself, but their lifestyle adapted in response. In particular, the balloon mycostrum is now able to form a kite-like balloon form, which allowed it to spread far and wide through the wind. Balloon knightworms take advantage of this for their own dispersal, including using it to cross the ocean into the north of Hydro. When doing so, the knightworm would simply dangle at the end of the mycostrum, suspended within it much as they're surrounded by mycostrum during their everyday life. Newly hatched balloon knightworms usually do so once old enough to leave the nest, being smaller and lighter, but adults disperse from time to time as well. This exerted a selective pressure for significantly smaller size; lacking competitors in this size range, their size reduced dramatically from that of the silk knightworm. When a balloon mycostrum develops into a balloon form, it may detach on its own, but it is more common for a balloon knightworm to sever it (using its antennae) and fly away on it, the act triggered by wind conditions.
When distinguishing a balloon knightworm from a silk knightworm, their symbiote is actually one of the most significant signs. It forms a frizz of strands that point upward, collecting especially between its host's antennae, a side effect of the genetic pathways that allow it to develop into its balloon form. Balloon knightworms rely on the mycostrum for survival and always have some on their body, as it provides insulation and keeps down their exoskeletal growth. They also live in nests made of mycostrum, which maintain a damp environment for their eggs as well. The female lays a semi-soft egg, which the male must fertilize before it hardens. They also rely on the nests as a warm, protected spot to hibernate in the winter.
Other changes include a flatter body and a joint in their ventral spikes. This isn't really for walking, as they still move mainly by inching along, but it allows them to tuck the spikes under their body when fitting through small spaces or when ballooning. This uses a similar genetic pathway to the joint in their antennae.
Balloon knightworms take better care of their mycostrums than their ancestors did. They'll use their antennae to cut up flora and then carry them to their nests, tucked in the mass of their symbiote. They especially use redcap mycostrums for this purpose: Being poisonous, the knightworms can't eat them, but there's nothing stopping them from using them to nourish their symbiotes.
Their mouthparts can only eat fairly soft food, preferably mycostrums, though they can handle other purple flora as well. Their antennae are useful for removing bits of food, but they can't slice through crystal flora.