I am currently designing evolution paths for tunicate which are a chordate invertebrate marine animal. In their larvae stage they are mobile and resemble tadpoles but in adult form some attach to hard surfaces and become sessile, whilst other free float and some remain with a similar design as the larval form.
Because of their larvae stage it is easy to see how their notochord could evolve into vertebrae and then have a similar evolution path as fish to amphibians but another interesting aspect about tunicate is that they are the only animal to produce cellulose.
From reading about high strength bioengineered materials from cellulose nanofibers it made me wonder if tunicates outer layer could be a cellulose exoskeleton and if it could possibly take an evolutionary path closer to arthropods?
Or could there be other biological adaptations that I have missed out?
What plausible biological adaptations could a tunicate evolve that will help them become a terrestrial animal, other than a vertebrate path similar to fish to amphibians? And is the cellulose exoskeleton a likely path that could lead them to evolve into forms similar to arthropods?