Reptiles (Reptilia) are a class that belongs to the subphylum of Vertebrates, in which we can find approximately 7,000 different species. Its name describes in Latin (repto) the way in which many of the reptile species move, either by sliding or crawling. While it is true that reptiles as a class have been very successful in both terrestrial and aquatic environments, we will cover in this section mainly aquatic reptile species, although the characteristics of this class of species are shared between species from both habitats. Among the aquatic reptiles we find species such as turtles, snakes, lizards and crocodiles.

The characteristic skin of the reptiles is covered by epidermal scales formed by keratin and can be optionally complemented with intradermal plates of a bony nature. Their body is generally robust and has strong extremities. In the head we find a moderately well developed brain. Its mouth usually has more or less developed teeth, which can replace several times (polyiodonts), although there are species such as turtles that lack teeth completely.

Another characteristic of reptiles is their ability to control body temperature. Although they are not species capable of controlling body temperature by their own means, they do manage to control it with the environment. In order to warm themselves, they lie down in the sun, thus capturing the heat. On the contrary, when they need to cool down, they move to shady areas or even submerge in water or underground.

Generally the species of reptiles have separate sexes. Mainly, fertilization occurs internally and after it the female lays the fertilized eggs in nests for incubation. It has been documented that various species of reptiles have the ability to determine the sex of their offspring based on the temperature at which the eggs from the clutch are incubated. Although this type of reproduction we have described is the majority, there are some species of lizards described as having the capacity for asexual reproduction by means of parthenogenesis.