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 gills.
This type of gill is most commonly observed on the aquatic larva of most species of salamanders, lungfish, and bichirs (which have only one large pair), and are retained by neotenic adult salamanders and some species of adult lungfish. They are present on non-transforming salamander species, such as most members of the family Proteidae (the olm and mudpuppies) and the family Sirenidae, which naturally never metamorphose into an air-breathing form. The embryos of frogs and caecilians also develop external gills at some point in their development, though these are either resorbed before or disappear shortly after hatching. Fossils of the distant relatives of modern amphibians, such as Branchiosaurus and Apateon, also show evidence of external gills.
The external gills commonly consist of a single stalk (rami) protruding from a gill arch behind the head of the animal, above an associated gill slit. The stalk usually contains muscle tissue, and may be moved by the animal as a free appendage, in order to stir up stagnant water. The stalk is lined by many thinly walled filaments (fimbriae), containing the majority of blood vessels used in gas exchange. Animals usually have one external gill originating on each gill arch (except the hyoid), which leads to there being three pairs of external gills in salamanders, and four in the gilled larvae of lungfish.
Externalgills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered...
Juvenile bichirs have externalgills, a very primitive feature that they share with larval amphibians. Previously, the evolution of gills was thought to have...
structure of a gill presents a large surface area to the external environment. Branchia (pl.: branchiae) is the zoologists' name for gills (from Ancient...
increase surface area for gas exchange. Four-gill slits lined with gill rakers are hidden underneath the externalgills, which prevent food from entering and...
involve gills, lungs, skin, and the membranes of mouth and throat. Larval salamanders breathe primarily by means of gills, which are usually external and...
retains it externalgills. Because skin and lung respiration alone is not sufficient for gas exchange, the common mudpuppy must rely on externalgills as its...
hatched, anuran tadpoles have externalgills that are eventually covered by skin, forming an opercular chamber with internal gills vented by spiracles. Depending...
Branchial arches, or gill arches, are a series of paired bony "loops" that support the gills in fish. As gills are the primitive feature of vertebrates...
Pokémon, Wooper is a creature resembling an axolotl, featuring blue skin, externalgills, and a flat tail. It eventually evolves into the Pokémon Quagsire. A...
still being made. With frogs and toads, the externalgills of the newly hatched tadpole are covered with a gill sac after a few days, and lungs are quickly...
Australian lungfish can breathe through its gills without needing air from its lung. In other species, the gills are too atrophied to allow for adequate gas...
externalgills much like those of newts. After two to three months, the young metamorphose into the adult form, losing their externalgills for gill openings...
neotenic, although the larval gills are small and functionless at first, and only adults have fully developed (but inefficient) gills. They are obligate air-breathers...
juveniles such as externalgills and small body size in what is known as neoteny. Dvinosaurians and the plagiosaurid Gerrothorax also retained gills, although...
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous...
rocks. Tadpoles have cartilaginous skeletons, gills for respiration (externalgills at first, internal gills later), lateral line systems and large tails...
hind feet. It exhibits neoteny, retaining larval characteristics like externalgills into adulthood, like some American amphibians, the axolotl and the mudpuppies...
the larvae bear externalgills, branching off from the gill arches. These are reduced in adulthood, their function taken over by the gills proper in fishes...
in 1946, these bones were considered to correspond to feather-like externalgills similar to those of modern-day neotenic salamanders, such as the mudpuppy...
reduced lungs, or no lungs at all. Larvae can sometimes have reduced externalgills if they live in cold and very oxygen-rich water. Fossils of hynobiids...
heads. They lay their eggs in cavities in the soil. The larvae have externalgills, and live in seepage areas until they metamorphose. The adults live...
black-and-white rhinophores somewhat resemble a rabbit's ears. Its externalgills are located near its rear. Its body is covered in papillae, fleshy protuberances...
teeth which are capable of biting humans The parapodia function both as externalgills (the animal's primary respiratory surfaces), and as means of locomotion...
from book gills, water-breathing structures among marine chelicerates. Although they have a similar book-like structure, book gills are external, while book...
parents build a nest for the young, which resemble tadpoles and have four externalgills. To enrich the oxygen in the nest, the male develops highly vascularized...
against predators. When they hatch, the young resemble tadpoles, with externalgills, and only later develop lungs and begin to breathe air. Until the introduction...
The larvae have externalgills, but after about four months these externalgills disappear and the lungs begin to work. One pair of gill slits is retained...
hellbender makes little use of these lungs and the juveniles lose their externalgills after around 18 months or about 125 mm in length. Hellbenders use their...
about 3 cm (1.2 in) long and externalgills remain until a length of about 20 cm (8 in) at an age of 3 years. The externalgills start to slowly decrease...
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