We explain everything about animals, their characteristics and how they are classified according to their body, their relationship with humans and their diet.
What are animals?
Animals or metazoans are living beings that make up the animal kingdom (Animalia), one of the four kingdoms of eukaryotic living beings (that is, organisms that have cells with a nucleus), and which are distinguished from plants, fungi and microorganisms. In general, animals are living beings endowed with their own and autonomous movement, a metabolism based on breathing and a nervous system that allows them to interact with their environment.
Animals as a whole are extremely diverse and are adapted to all habitats on the planet, establishing different types of relationships with each other and with other living beings. Humans also belong to the animal kingdom, but since they are the only living beings known to have their own consciousness and articulate language, they are generally given a separate philosophical category within the group of animals. Seen in this way, a human being would be an animal with language. You must read about Umbanda once.
Animals appeared on the face of the Earth approximately 542 million years ago, during the so-called “Cambrian explosion” or evolutionary radiation of the Cambrian.
It is not known exactly what the reasons were for such a massive and abundant diversification of life at that time. However, it is known that of the approximately 20 phyla or groups of animal species known to date, at least 11 originated in that specific time, that is, the first and oldest multicellular animal species emerged there, whose descendants can still be found on the planet.
The word “animal” comes from the Latin animalis, which can be translated as “being endowed with breath” (i.e., anima), that is, “creature that breathes.” The science that studies animals is called zoology, and it is a specific branch of biology that allows animals to be classified according to different categories, based on traits such as their behavior, anatomy, or even their relationship with humans. Maybe you should definitely read about Selfie once.
General characteristics of animals
The main general characteristics of animals are:
- They are eukaryotic living beings, that is, they have cells with a well-defined cell nucleus, in which the genetic information is gathered; and also multicellular, that is, whose bodies are made up of more than one cell.
- Unlike plants and fungi, animal cells do not have a cell wall (but a more flexible plasma membrane), nor vacuoles, nor plasmodesmata.
- Their nutrition is heterotrophic, that is, they obtain their nutrients from the organic matter of other living beings, unlike plants (autotrophs). For this reason, animal cells also do not have chloroplasts (organelles for photosynthesis), but lysosomes.
- Their metabolism is aerobic, that is, it requires a continuous supply of oxygen (since it obtains its energy from the oxidation of organic molecules). The process of capturing oxygen from the environment (either air or water) is known as respiration and, therefore, all animals breathe.
- In the vast majority of cases, they are equipped with their own and autonomous mobility, that is, they can change their environment at will, thanks to the presence of motor organs such as cilia, legs, fins, wings, among others.
- They are sexual species, that is, with predominantly sexual reproduction. This type of reproduction requires a male and a female to produce a new individual, through the union of their well-differentiated sexual cells or gametes. There are, however, some animal species capable of asexual reproduction in certain circumstances.
- Their bodies are composed of collagen, a structural protein found in all the fibers of their tissues. The latter, in addition, usually have a very high level of differentiation and specialization.
- Their bodies present bilateral symmetry: they can be divided with a transverse line into two identical and corresponding halves. The exception to this rule is made up of a few primitive phyla such as poriferans and echinoderms.
Vertebrate animals and invertebrate animals
The animal kingdom can be divided into two large groups, depending on the presence of an internal skeleton in their bodies, which includes a skull and a spinal column. Thus, we can talk about:
Vertebrate animals
Those that have an internal skeleton with a spinal column and a skull, all made of bone tissue (bone) and designed to protect the nervous system: the spinal cord and the brain. Their bodies are also easily divided into three segments: head, trunk and limbs.
Examples of vertebrate animals are mammals, fish, reptiles, birds and amphibians. Vertebrate species include humans, dogs, horses, crocodiles, mice, bats, platypuses, birds, frogs, among many others.
Invertebrate animals
Those that have an external skeleton (exoskeleton) like armour made of chitin. Therefore, they do not have vertebrae or a skull, and most of them are oviparous animals (they are born from eggs). In evolutionary terms, they are more primitive than vertebrates.
Examples of vertebrate animals are insects and arthropods, mollusks, sponges, cnidarians, annelids and echinoderms. Among the invertebrate species are sea urchins, octopuses, bees, scorpions and spiders, earthworms, starfish, among many others.
Wild animals and domestic animals
Depending on their relationship with humans and society, animals can be classified into two groups, depending on whether or not they are domesticated, that is, whether they have adapted to peaceful coexistence with humans, or not. Thus, we can distinguish between:
Wild animals
Those that are unaware of the presence of humans or are not at all accustomed to it, and therefore react to it with aggression or other instinctive behaviors. Animals that live in nature are all wild.
Examples of wild animals are: wolves, lions, blue whales, condors, rhinoceroses, hippos, penguins, polar bears, most snakes, and all those animals that exist within human society only in zoos.
Domestic animals
Those that have adapted over time (and the direct intervention of our species) to interact with humans and even to depend on them, occupying a stable place within civilization. Pets, farm animals, and trained animals are all domestic.
Examples of domestic animals are: cow, dog, cat, chicken, sheep, goat, horse, pigeons, hamsters, some species of fish and turtles, among others. You must read about Hashtag once.
Carnivorous animals, herbivorous animals and omnivorous animals
Animals are heterotrophic beings, which must consume the organic matter of other living beings in order to survive, that is, feed on other living beings and organic matter. But not all of them do it in the same way, and depending on their food preferences, it is possible to classify them into three categories:
Carnivorous animals
Those whose diet consists strictly or almost strictly of meat, that is, of the bodies of other animals. This means that the vast majority are predators (which attack and devour other animals) or scavengers (they feed on their corpses once the predators have finished eating). Carnivorous animals usually have sharp teeth to tear the meat and limbs provided with sharp claws to help them when hunting.
Examples of carnivorous animals are: the lion, the wolf, the tiger, the shark, the snake, the eagle, among others.
Herbivorous animals
Those whose diet is composed strictly or almost strictly of plant substances and fungi, that is, of parts of the body of plants and fungi or of materials produced by them. Herbivores usually have flat teeth with strong molars, to grind plant matter, as well as various stomachs to digest them more efficiently.
Examples of herbivorous animals are: the cow, the horse, the sheep, the giraffe, the ox, the rhinoceros, butterflies, among others.
Omnivorous animals
Those whose diet is diverse, adaptable to availability or occasion, and therefore combine foods of plant origin with foods of animal origin. They are animals with a changing or multiple diet, which can play different food roles at the same time, being herbivores and carnivores at the same time. Omnivores usually have mixed teeth, which combine sharp teeth for tearing and blunt molars for crushing.
Examples of omnivorous animals include: humans, monkeys, rats, pigs, bears, foxes, turtles, crows, among others.
