Teleostomi is a grouping of fish in the Gnathostomata ('jawed fish'). It contains the extinct Acanthodii ('spiny sharks'), and the Osteichthyes ('bony fish'). Teleostomi have two adaptations which relate to their respiration: First, they had some kind of operculum (a set of bones which cover the gills). The also developed a primitive lung. As of 2020, there is no agreement, as to the level of the grouping. Some people see it as a clade, others say it is a crown group.