Chondrostei
This group has at times been classified with the sharks: the similarities are obvious, not only do the chondrosteans mostly lack bone, the structure of the jaw is more akin to that of sharks than other bony fish. Both lack scales (except the Polypteriforms). Additional shared features include spiracles and, in sturgeons, a heterocercal tail (the vertebrae extend into the larger lobe of the caudal fin). However the fossil record suggests that these fish have more in common with the Teleostei than their external appearance might suggest.