Animals make up a kingdom of over one million species. However, fossils found reveal that a much larger number of animal species have lived on Earth but are now extinct.
We living things are many and come in many shapes and sizes - from microscopic bodies like the mite to gigantic bodies like the blue whale. Some with simple shape, organization and functioning of the body, like a sea sponge; others with the complex structure of a mammal.
Electron microscopy of mites measuring about 0.2 to 0.5mm being very difficult to see with the naked eye
Beached Blue Whale
Despite the great diversity, almost all animals have one common feature: they are made up of thousands of cells of various types. Another aspect common to beings in the Animal kingdom is that they get their food from other living things.
Animals inhabit almost every known environment on our planet, and can be found both at high altitudes in the mountains and in deep sea pits.
Most species are capable of moving, that is, moving the body from one place to another. However, there are species that live fixed, that is, sessile, in the environment, such as sea sponges.
The animals are studied by zoology - field of science whose name comes from the Greek language: zoo means "animal", and logia, "study".
To facilitate the study, it is important to classify the animals. One way to make this classification is to divide them into two large groups: vertebrates and invertebrates.
In the group of vertebrates there are animals that, like humans, have a spine. Already the group of invertebrates It is formed by those who have no spine.
THE spine It is a type of skeletal axis formed by articulated parts - the vertebrae -, which can be bone or cartilage. At joints allow for flexibility of the internal skeleton, facilitating movement.
Observe the spine of the man and in detail the articulation between the vertebrae.
In yellow the vertebrae and in blue the joint that allows movement.
The spine, associated with the muscular system, ensures that animals move around and maintain their firm structure.