Reptiles look quite like Amphibians, but have something more: they can also live in dry areas, far from water. Actually, the animals that best represent the entire class are snakes, but Reptiles also include such quadrupeds as tortoises and crocodiles. ReptilesThe word 'reptile' comes from the Latin reptilis, which means 'creeping'. Finally, the tail is completely swallowed up into the body. During the metamorphosis, the tadpole begins to grow legs and its gills become smaller and smaller until they disappear: they are replaced by lungs, that are necessary to breath air. From the eggs wriggle out the young animals, called tadpoles and looking like small fish: later on, the tadpole from a larva becomes a fully formed adult. Before becoming adults, they undergo changes that completely transform their appearance. If instead the eggs are held inside the female's body until the hatching, the fish are called 'ovoviviparous'.ĪmphibiansThe word 'amphibian' comes from the Greek and means 'double life', since these animals live partly in water and partly on land. In this case, the fish are called 'oviparous', which means the embryo develops inside the egg after having been laid by the female. Fertilisation is mostly external: the female lays its eggs and the male fertilises them by coating them with its sperms. Fish produce a huge number of eggs, since they have to go through many dangers and few can survive: cods lay up to six million eggs at a time. the body weight/volume ratio) to swim up and down without moving its fins. A typical organ of most, but not all, fish is the air bladder, which is filled with gas and allows therefore the fish to change its specific gravity (i.e. Their appearances can be the most diverse, depending on how they have adapted to the environments in which they live. These animals have a bone internal skeleton, mainly made up of living material that grows with the animal until it reaches its definitive dimensions.įish have been the first vertebrates to have appeared on the Earth. Connected to the vertebra are the muscles that allow the movement of the different parts of the spine.

Between the vertebra are the cartilage disks, that make the spine a flexible bone structure. The vertebrates are characterized by a spine, or backbone, consisting of vertebra that surround the nerve cord. Vertebrates include some of the biggest organisms that have ever lived on Earth and our species also belongs to them Despite their limited differences and the modifications in time, the vertebrates have conquered on just emerged lands, but also the sky. All the vertebrates (Vertebrata), instead, have a similar body. The numerous invertebrates’ phyla are characterized by a wide range of shapes and way of living.

Does a shark have a backbone