Each gill bar may be extended by gill septa. Most bars have gill rakers on their pharyngeal margins. Typical gills-two rows of gill filaments . Capillary beds in lamellae between the loops. Small barrier between blood and water.
Fine mesh slows water down.
Gills also important in excretion and osmoregulation . Pouched gills . Charactgeristic of Agnatha. Gill filaments in pouchlike chambers. Septal gills .