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Actinopterygian node J: The skull's ethmoid region is lengthened, elongated ascending process of the parasphenoid.
Actinopterygian node K (defining node of the "CHONDROSTEI"): Palatoquadrate bones meet anteriorly in midline, large and blade shaped hyomandibular, absence of suborbital bones, reduced or absent preopercular, opercular and gulars, reduced body scales, peg and socket articulation generally absent from dermal scutes.
The acipenserids - or sturgeons - are a primitive group of large (reaching one to six metres in length) extant northern fish. These have greatly reduced bony skeletons, having secondarily reverted to mainly cartilaginous ones. The scales have also been reduced to five rows of large plates of dermal bony elements. Acipenserids have retained a single air sac as a floatation device, and do not breathe air. These fish spend most of their lives feeding on the sea floor (going upriver only to lay their eggs), restricting the use of the lung function of their air sac, which probably accounts for its loss.