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However, the axolotl is unusual in that it has a lack of thyroid-stimulating hormone, which is needed for the thyroid to produce thyroxine in order for the axolotl to go through metamorphosis; therefore, it keeps its gills and lives in water all its life, even after it becomes an adult and is able to reproduce. Neoteny is the term for reaching ...
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 ...
The density of the water prevents the gills from collapsing and lying on top of each other, which is what happens when a fish is taken out of water." [7] Higher vertebrates do not develop gills, the gill arches form during fetal development, and lay the basis of essential structures such as jaws, the thyroid gland, the larynx, the columella ...
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Axolotls retain gills and fins as adults; these are juvenile features in most amphibians. Paedomorphosis can be the result of neoteny , the retention of juvenile traits into the adult form as a result of retardation of somatic development, or of progenesis, the acceleration of developmental processes such that the juvenile form becomes a ...
Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first ...
Mexico's axolotl salamander faces a doomsday scenario battered by decades by dirty water, ravenous non-native fish and the steady encroachment of one of the world's biggest megacites. Chris Dignam ...
The gills' large surface area tends to create a problem for fish that seek to regulate the osmolarity of their internal fluids. Saltwater is less dilute than these internal fluids, so saltwater fish lose large quantities of water osmotically through their gills. To regain the water, they drink large amounts of seawater and excrete the salt.