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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 ...
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 ...
All but one species bury in the mud when the body of water they live in dries up, surviving up to two years until water returns. Bichir (Polypteridae): These 12 species are the only ray-finned fish to retain lungs. They are facultative air breathers, requiring access to surface air to breathe in poorly oxygenated water. [1]
In fish a countercurrent flow (lower diagram) of blood and water in the gills is used to extract oxygen from the environment. [6] [7] [8] All basal vertebrates breathe with gills. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the esophagus to the exterior.
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Neotenic axolotl, showing external gills. Not all species of salamanders follow this path. Neoteny, also known as paedomorphosis, has been observed in all salamander families, and may be universally possible in all salamander species. In this state, an individual may retain gills or other juvenile features while attaining reproductive maturity.