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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.
A number of features distinguish the plethodontids from other salamanders. Most significantly, they lack lungs, conducting respiration through their skin, and the tissues lining their mouths. [3] Some species of cave salamanders are neotenic, and keep their larval gills even as adults. Gills are absent in all other adult plethodontids. [13]
In the lungless salamanders (family Plethodontidae and the clawed salamanders in the family of Asiatic salamanders), no lungs or gills are present, and gas exchange mostly takes place through the skin, known as cutaneous respiration, supplemented by the tissues lining the mouth. To facilitate this, these salamanders have a dense network of ...
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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. When the salamander performs the "suck and gape" feeding style, the prey is pulled into the mouth, and the teeth function to hold the prey inside the mouth and prevent the prey ...
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 ...
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]
P. ruber. In the Plethodontidae (lungless salamanders), many members respire through their skin and the lining in their mouths. Lunglessness in this family may have evolved due to an adaptation for life in streams, and members of the family Plethodontidae probably did evolve other methods for respiration other than lungs (i.e. gills) due to enhanced survival of larval salamanders in fast ...