Siren (amphibian)
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The Sirens are a family of aquatic salamanders. They have small front extremities and lack hind ones. In one species the skeleton in their front limbs are even made of cartilage only. In contrast to most other salamanders they have external gills bunched together on the neck not only in larvae state, but also in adulthood. If the conditions of a pond are not suitable, these gills will shrink to mere stumps while the siren is still in larvae form, and may not function at all. [1] The Sirens are limited to North America.
Sirens feed mainly on worms, small snails, shrimp, and filamentous algae. [2]
At least two of the species can produce vocalizations.
Sirens are quite distinct from other salamanders, hence they form their own suborder Sirenoidea of the Caudata order. Sometimes they are even referred as a completely distinct order Meantes or Trachystomata. Genetic analysis also confirms that the Sirens are not closely related to any other Salamander groups. Many of their unique characters seems to be partly primtive and partly derived.
Unlike other salamanders, an interventricular septum is present in the heart.
Like the suborder Cryptobranchoidea they most likely have external fertilization.
Just like congo eels, they are probably able to cross land on moist nights through wet grass.
The combined biomass of lesser siren in a Texas pond exceeded the total biomass of the pond's seven species of fish.[citation needed]
They are not primitive as one may think, but degenerated. The larval gills are small and functionless at first, and only the adults have fully developed gills in form and function. Because of this it is most likely they have evolved from a terrestrial ancestor that still had an aquatic larval stage.
Except from some patches of small teeth on their palate and on the splenial bone on the inner side of their lower jaw, their mouth has lost all the teeth and have been replaced with a horny sheath that resemples a beak.
Like most lungfishes, they are able to burrow down into the mud at the bottom of drying ponds and become entombed, covering themselves with a cocoon. In this period they are breathing with their small but functional lungs instead of their gills.
The Siren family (Sirenidae) is subdivided into two genera, with two species each:
- Dwarf sirens (Pseudobranchus)
- Southern Dwarf Siren (Pseudobranchus axanthus)
- Northern Dwarf Siren (Pseudobranchus striatus)
- Sirens
- Lesser Siren (Siren intermedia)
- Greater Siren (Siren lacertina)
[edit] References
- San Mauro, Diego; Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer (May 2005). "Initial diversification of living amphibians predated the breakup of Pangaea". American Naturalist 165: 590-599.
