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Sirenidae |
| Sirens | ||||||||||||||
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The Sirenidae, or sirens, are a family of aquatic salamanders. Family members have very small fore limbs, and lack hind limbs altogether.1.In one species, the skeleton in their forelimbs is made of only cartilage. Sirens are found only in the south-eastern United States, and northern Mexico.1 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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Sirens are quite distinct from other salamanders, 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.
Sirens are generally eel-like in form, with two tiny, but otherwise fully-developed, fore limbs. They range from 25 centimetres (9.8 in) to 95 centimetres (37 in) in length.1 They are neotenic, although the larval gills are small and functionless at first, and only adults have fully-developed gills. Because of this, it is most likely sirens have evolved from a terrestrial ancestor that still had an aquatic larval stage. Like amphiumas, they are able to cross land on rainy nights.
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.2
If the conditions of a water source are unsuitable, a larva 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 encase themselves with a cocoon of mucus to survive periods of drought.1 During such periods, they breathe with their small but functional lungs.
Unlike other salamanders, an interventricular septum is present in the heart. At least two of the species can produce vocalizations. The structure of sirens' reproductive systems suggests that they employ external fertilisation.1
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
The siren family (Sirenidae) is subdivided into two genera, with two species each:
Family SIRENIDAE
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