How do the pouchlike gills of agnathans differ from the gills of jawed fishes?

Agnathans (jawless fishes) and gnathostomes (jawed fishes) possess distinct respiratory structures. Unlike the slitlike gills found in jawed fishes, the gills of agnathans are pouchlike and open to the surface through pores.1

In agnathans, these gills are contained within pouches that may open individually to the surface through separate pores, or in some species, they may open into a common duct that leads to a single external pore. In contrast, jawed fishes typically possess gill arches that support the respiratory apparatus, and in advanced bony fishes, these structures are protected by a single, movable bony covering known as the operculum.23