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Molecular changes in the mudpuppy during post-embryonic development primarily due to the thyroid gland prevent the internalization of the external gills as seen in most salamanders that undergo metamorphosis. [34] The external gills seen in salamanders differs greatly from that of amphibians with internalized gills.
The lungs of an axolotl, though present alongside gills after reaching non-metamorphosed adulthood, develop further during metamorphosis. [ 46 ] An axolotl that has gone through metamorphosis resembles an adult plateau tiger salamander , though the axolotl differs in its longer toes.
Metamorphosis is then complete with loss of gills and gill slits, along with pigment changes. [9] This is typically a 4-6 month larval stage. The effects that elevation has on larval stages have been studied extensively showing that at lower elevations larvae metamorphosized sooner than those at higher elevations which had delayed metamorphosis ...
[15] [16] The common mudpuppy never leaves its aquatic environment and therefore does not undergo morphogenesis; however, many salamanders do and develop differentiated teeth. [17] Aquatic salamander teeth are used to hinder escape of the prey from the salamander; they do not have a crushing function. [17] This aids the salamander when feeding.
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 ...
This results in adults that have long, heavily filamented external gills, gill slits lined with tooth-like gill rakers, and caudal fins. When stressed , Ambystoma dumerilii can undergo an incomplete metamorphosis , though this is process significantly decreases their lifespan and is often fatal.
[7] [8] Alongside E. nerea, E. braggi, and the West Virginia spring salamander, the western grotto salamander is the only cave salamander which undergoes metamorphosis. The adult form is pinkish white, sometimes with traces of orange on its tail, feet, and sides, and has 16–19 costal grooves.
The greater siren is the third longest salamander in the Western Hemisphere. [4] S. lacertina is paedomorphic, as are all sirens. They lack hindlimbs as well as a pelvic girdle, and have external gills all throughout their lives along with small lungs. They lack eyelids, and have an unfused pectoral girdle. [5]