Siren (amphibian)
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- Not to be confused with order Sirenia (manatees and dugongs)
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The sirens are a family of aquatic salamanders. Family members have small front extremities and lack hind limbs.[citation needed] In one species, the skeleton in their forelimbs is made of only cartilage. Sirens are limited to the North American continent.[citation needed] In contrast to most other salamanders they have external gills bunched together on the neck in both larval and adult states.
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[edit] Description
Sirens are quite distinct from other caudates, hence they form their own suborder Sirenoidea. Sometimes they are even referred as a completely distinct order (Meantes or Trachystomata). Genetic analysis confirms that sirens are not closely related to any other salamander group.[citation needed] Many of their unique characteristics seem to be partly primitive and partly derivative.
They are not primitive as one may think, but degenerated.[citation needed] The larval gills are small and functionless at first, and only adults have fully-developed gills in form and function. Because of this, it is most likely sirens have evolved from a terrestrial ancestor that still had an aquatic larval stage. Like amphiumas (congo eels), they are probably able to cross land on moist nights through wet grass.
Except for 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 dentition and has been replaced with a horny sheath that resembles a beak. Sirens feed mainly on worms, small snails, shrimps, and filamentous algae. [1]
If the conditions of a water source are unsuitable, a larvae will shrink its gills to mere stumps, and may not function at all. [2] They are also able to burrow into mud of drying ponds and become entombed, covering themselves with a cocoon. In this period they breathe with small but functional lungs.
Unlike other salamanders, an interventricular septum is present in the heart. At least two of the species can produce vocalizations. Like the suborder Cryptobranchoidea, siren members are most likely external fertilizers.
The combined biomass of Siren intermedia species in a Texas pond exceeded the total biomass of the pond's seven species of fish.[citation needed]
[edit] Taxonomy
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] See also
[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.
- ^ John Farrand Jr., The Audubon Society Encyclopedia of Animal Life, 1982
- ^ John Farrand Jr., The Audubon Society Encyclopedia of Animal Life, 1982
[edit] External links
