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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 ...
Instead of internal gills, they develop three feathery external gills that grow from the outer surface of the gill arches. Sometimes, adults retain these, but they usually disappear at metamorphosis. Examples of salamanders that retain their external gills upon reaching adulthood are the olm and the mudpuppy.
Marine teleosts also use their gills to excrete osmolytes (e.g. Na⁺, Cl −). The gills' large surface area tends to create a problem for fish that seek to regulate the osmolarity of their internal fluids. Seawater contains more osmolytes than the fish's internal fluids, so marine fishes naturally lose water through their gills via osmosis.
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.
The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and then around the body in a single circulatory loop. [3] The eyes are adapted for seeing underwater and have only local vision. [definition needed] There is an inner ear but no external or middle ear.
These regress upon adulthood, their function taken over by the gills proper in fish, or by lungs (which are homologous to swim bladders) and cutaneous respiration in most amphibians. Some neotenic amphibians (such as the axolotl ) retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being ...
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 external gills will eventually be hidden by a layer of skin. Tadpoles of frogs and toads are usually globular, with a laterally compressed tail with which they swim by lateral undulation . When first hatched, anuran tadpoles have external gills that are eventually covered by skin, forming an opercular chamber with internal gills vented by ...