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External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. Instead, the respiratory organs are set on a frill of stalks protruding from the sides of an animal's head. The axolotl has three pairs of external ...
Young amphibians generally undergo metamorphosis from an aquatic larval form with gills to an air-breathing adult form with lungs. Amphibians use their skin as a secondary respiratory interface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin.
Many invertebrates, and even amphibians, use both the body surface and gills for gaseous exchange. [3] Gills usually consist of thin filaments of tissue, lamellae (plates), branches, or slender, tufted processes that have a highly folded surface to increase surface area. The delicate nature of the gills is possible because the surrounding water ...
These are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods. [12]
Young amphibians generally undergo metamorphosis from an aquatic larval form with gills to an air-breathing adult form with lungs. Amphibians use their skin as a secondary respiratory interface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin.
It goes through paedomorphosis and retains its external gills. [4] Because skin and lung respiration alone is not sufficient for gas exchange, the common mudpuppy must rely on external gills as its primary means of gas exchange. [5] It is usually a rusty brown color [6] and can grow to an average total length (including tail) of 13 in (330 mm). [7]
Only occasionally leaving the water, the hellbender makes little use of these lungs and the juveniles lose their external gills after around 18 months or about 125 mm in length. [17] [18] Hellbenders use their lungs for buoyancy more than breathing. [14] It is blotchy brown or red-brown in color, with a paler underbelly.
In amphibians and some primitive bony fish, the larvae bear external gills branching out from the gill arches. [3] These regress upon adulthood, their function taken over by the gills proper in fish, or by lungs (which are homologous to swim bladders) and cutaneous respiration in most amphibians.