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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 ...
Sirenidae, the sirens, are a family of neotenic aquatic salamanders. Family members have very small fore limbs and lack hind limbs altogether. [1] In one species, the skeleton in their fore limbs is made of only cartilage. In contrast to most other salamanders, they have external gills bunched together on the neck in both larval and adult
[15] [16] The common mudpuppy never leaves its aquatic environment and therefore does not undergo morphogenesis; however, many salamanders do and develop differentiated teeth. [17] 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.
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 ...
Greater siren out of water. Greater sirens are carnivorous and prey upon invertebrates (such as insects, crustaceans, gastropods, bivalves, spiders, molluscs, and crayfish) [11] and aquatic vertebrates (such as small fish) [11] with a possible preference for molluscs (such as snails and freshwater clams), [8] [12] although they have been observed to eat vegetation such as algae.
In salamanders, sexual size dimorphism is usually female-biased, but in Siren intermedia, it's the opposite. Males are the larger sex, and they also have significantly larger heads and enlarged masseter muscles than females. [4] Lesser sirens are notably neotenic, and possess external gills throughout their lives. [3]
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]
Like in the majority of salamander species, there are four toes on the fore limbs and five on the hind limbs. They have paedomorphic traits, meaning their metamorphosis from the larval stage is incomplete, so they lack eyelids and the adults retain gill slits (open in the hellbender, closed in Andrias).