Are there any other kind? 
There could be, it just doesn’t seem to have happened here. That is, there’s no particular reason why some group of organisms outside of the chordates might not have developed internal supporting structures similar to - albeit developmentally different from vertebrate bones - in the same sort of way that other similar structures have arisen in parallel in unrelated groups of organisms.
It just didn’t chance to occur here.
Cuttlebones probably don’t really count.