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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 ...
These internal gills and operculum are not homologous with those of fish, [108] and are only found in tadpoles as both salamanders and caecilians have external gills only. [109] Combined with buccal pumping the internal gills has allowed tadpoles to adopt a filter feeding lifestyle, even if several species have since evolved other types of ...
Tadpoles of amphibians have from three to five gill slits that do not contain actual gills. Usually no spiracle or true operculum is present, though many species have operculum-like structures. Instead of internal gills, they develop three feathery external gills that grow from the outer surface of the gill arches.
The external gill rami are lined with filaments (fimbriae) to increase surface area for gas exchange. [15] Four-gill slits lined with gill rakers are hidden underneath the external gills, which prevent food from entering and allow particles to filter through. Axolotls have barely visible vestigial teeth, which develop during metamorphosis.
Juvenile bichirs have external gills, a very primitive feature that they share with larval amphibians. Previously, the evolution of gills was thought to have occurred through two diverging lines: gills formed from the endoderm, as seen in jawless fish species, or those form by the ectoderm, as seen in jawed fish.
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]
The animal measured roughly 1.6 inches (4 centimeters) long on average and had a flattened, sinuous body and a tiny head, tipped with two tentacles and fringed with external gills.
The external gills seen in salamanders differs greatly from that of amphibians with internalized gills. Unlike amphibians with internalized gills which typically rely on the changing of pressures within the buccal and pharyngeal cavities to ensure diffusion of oxygen onto the gill curtain, neotenic salamanders such as Necturus use specified ...