Amphibians & Reptiles
Amphibians, formerly known as amphibians, form a class of tetrapod vertebrates. By their way of life, amphibians (from the Greek amphi, on both sides, and bios, life) are at the crossroads between the aquatic environment and the terrestrial environment.
In today's wild, Amphibians are represented by three groups :
- Anurans (frogs and toads)
- Urodeles (salamanders and newts)
- and the Gymnophiones (apodes)
In addition to their dependence on the aquatic environment, amphibians have bare skin. If the larvae breathe using gills, adults use their lungs, with the exception of a taxon of salamanders which breathe through the skin.
Amphibians have skin covered with glands and devoid of scales. The glands produce secretions, including toxins, which prevent bacteria and fungi from growing on their skin, as well as bitter substances intended to repel predators. Amphibians do not breathe only with their lungs. Their very thin skin also allows oxygen to be exchanged with air. A third possibility is the exchange of oxygen through the oral mucosa, which is why batrachians are regularly observed to perform a rapid movement of the throat from bottom to top. Amphibians do not drink. Fluid absorption also takes place through the skin.
Amphibians have a larval and an adult stage, with very distinct circulatory systems. In the larva, the circulation is similar to that of a fish, and the heart composed of two compartments sends blood to the gills where it is oxygenated, before it crosses the rest of the body and returns to the heart, forming only one loop. In adults, amphibians, including frogs, lose their gills and develop lungs.
The name reptiles designates terrestrial animals at variable temperature, with bodies often elongated and covered with scales, and whose gait, legs apart and body close to the ground, is close to crawling. Reptiles are so-called cold-blooded animals, or poikilotherms, that is to say that their internal temperature is not stable but dependent on that of the external environment.
Reptiles have four distinct orders :
- crocodilians (crocodiles, gavials, caimans and alligators) consisting of about 30 species.
- Rhynchocephalans (New Zealand sphenodons) having only two distinct species.
- squamates (lizards, snakes and amphisbenes) family made up of approximately 9,900 species.
- testudines (turtles) made up of around 340 species.
Reptiles are amniotes. They are mainly oviparous but some are ovoviviparous. In oviparous species, sex is often determined by environmental conditions, including temperature. There are three modes of fertilization in reptiles:
- oviparous reptiles: the young come out of the eggs laid by their mothers (this is the case among others for turtles and for lizards in our regions).
- ovoviviparous reptiles: the eggs hatch immediately after laying.
- ovoviparous reptiles: the eggs hatch in the mother's body (the viper).
The study dealing with reptiles is called herpetology.