External gills

• External gills develop from the outer wall of the pharynx or the exposed portion of the branchial arch.
• They occur in larval lampreys, few larval fishes, Polypterus, lungfishes, some larval teleosts, and all larvae and some adults of amphibians.
• There is a single pair of larval gills in the chondroitin bony fish, Polypterus, which has a long axis carrying gill lamellae.
• The African and South American lungfishes possess 4 pairs of feathery external gills.
• The larval forms of some amphibians and some adult urodeles possess external gills that arise simply as folds of skin on the surface of the III, IV, and V branchial arches but are easily supported by the skeletal system.
• The larvae of limbless amphibian, Caecilia, have a pair of exceptionally large leaflike gills with profuse blood supply.