The class of the Amphibians ( Amphibia ), in the past “batrachians”, is a class of Vertébré S Tétrapode S, intermediary between the fish with fleshy fins and the Sauropsida in the conquest of the terrestrial life.

General information

The majority of the Amphibians have a phase of aquatic life (Larve S) and a terrestrial phase of life after a metamorphosis controlled by the thyroid hormones. This metamorphosis is accompanied by the loss of the tail in the Amphibians belonging to the class of the Anoure S and the development of the members. Except very rare exceptions ( Arenophryne rotunda ), the adults of the species best adapted to the air life must return towards the aquatic environment of fresh water to lay eggs. There is coupling in general but without internal fecundation, the male pouring its sperm at the time when the female lays its eggs. There exist however exceptions such as for example the majority of the salamander S, Amphibians about the Urodèle S, where the female after an internal fecundation preserves the embryos and the larvae in the genital ways (case of Viviparité). There exist cases of Néoténie as for example at the Axolotl which reproduces in a larval state and do not metamorphose themselves.

The Amphibians are Poïkilotherme S, i.e. they cannot control the temperature of their body, and are thus dependant on the external thermal conditions (their internal temperature is variable). The adults breathe thanks to their Poumon S sacculaires, and with their skin (Cutaneous respiration) fine (slightly keratinized), richly vascularized and often covered of Mucus (allows the dissolution of gases, the limitation of dehydration and possibly contains Toxine S to defend oneself, especially at the tropical species). The larva has Branchie S, external during the first internal times then.

The Amphibians appeared on ground with the Dévonien, period of the primary era, approximately 370 million years ago and were represented in particular by the group of the Stégocéphales. Nowadays, one counts nearly 6.000 Espèce S of Amphibians.

Systematic

Phylogeny

─o Sarcopterygii ├─o Coelacanthimorpha or Actinistia └─o ├─o Dipnoi (+) └─o Tetrapoda ├─o Amphibians + ( Lissamphibia and Lepospondyli ) └─o ├─o Temnospondyli (extinct) (+) └─o Reptiliomorpha └─o Cotylosauria └─o Amniota (+)

The order Paraphylétique of the Labyrinthodontia , formerly classified in the Amphibians, must be regarded as obsolete.

Classification of the Amphibians

The few 6.000 known species of Amphibians are divided into three orders: The Anoura, Urodela and Gymnophiones.

See too

Ecological threats

See also: Decline of the populations of Amphibians

A dramatic decline of the populations of Amphibians, in particular of disappearances of populations and local exctinctions, were indexed during the two last decades throughout the world. Several causes are advanced, like the destruction of the natural habitats and their modification, the overexploitation of certain populations, pollution, the introduction of concurrent species, the climate change, the destruction of the Couche of ozone (ultraviolet radiations were shown particularly harmful for the skin, the eyes and eggs of the Amphibians) and of the diseases.

Because of the many threats which weigh on them, of very many species are classified as being in danger by IUCN. The international scientific community starts to become aware of the extent of the disaster and tries to set up plans of protection of the threatened species.

See too

Amphibian

Related articles

External bonds

  • Company Herpétologique de France
  • Site of Declining Amphibian Population Task force
  • Site of the team of protection of the Amphibians, Species Survival Commission
Breeding:
  • Amphibians on the site of the Canadian Council of protection of Animals.

Simple: Amphibian Zh-min-nan: Lióng-chhe-lūi

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