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Why are sirens unusual among salamanders?
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Caudata
Tiger salamanders (Ambystoma tigrinum) are widespread across much of the United States. Although they are generally black with yellow blotches, bars, spots, or even stripes, some are lighter in colour or have olive markings. Tiger salamanders belong to the mole salamander family, Ambystomatidae.
Sirens (family Sirenidae) are considered unusual among salamanders due to several distinct physical and biological characteristics:
- Morphology: Unlike typical four-legged salamanders, sirens have long, slender, eel-like bodies that lack hind legs and a pelvis, possessing only tiny forelegs.12
- Paedomorphosis: Sirens exhibit an extreme form of paedomorphosis, meaning they retain larval features—such as feathery gills—throughout their entire lives rather than undergoing metamorphosis.13
- Reproductive Biology: While most salamanders utilize internal fertilization via a spermatophore, the reproductive habits of sirens remain largely unknown. They are unusual because males lack the cloacal glands necessary to produce spermatophores, and females lack the spermathecae used for sperm storage. Furthermore, they lay eggs singly, a behavior that is not typically facilitated by external fertilization.3
These traits distinguish them from the majority of the order Caudata, which generally transition from aquatic larvae to terrestrial or semiterrestrial adults.32