Hi,can i ask something again?where do the chondrostean fish,like bichir and sturgeon belong?do they belong to osteoichthyes or chondrichthyes?if so,why?thanks

They belong to Osteoicthyes, despite mostly being cartalaginous! Chondrostei is no longer considered a valid group, and has been based on lots of different groups of osteoicthyes fish that have separately lost most of their ossification (bones) and so superficially resemble each other and members of Chondrichthyes, which are also cartilaginous. The exact place of sturgeons and paddlefish, the acipenseriformes, on the tree of life is uncertain at the moment, but nearly all DNA analyses place them in Osteoicthyes rather than Chondrichthyes...