animal kingdom

Animals

2022

We explain what the animal kingdom is, its origin and characteristics. Also, how is its classification, taxonomy and examples.

About two million different species belong to the animal kingdom.

What is the animal kingdom?

The animal kingdom or animalia constitutes, together with vegetal kingdom, fungi, protists Y moneras, one of the possible ways in which biology classifies known life forms. It is one of the great traditional kingdoms, despite the fact that the classification has varied markedly over more than 200 years of classification attempts.

The creatures contained in this kingdom are called animals, and are characterized by enormous ecological, morphological and behavioral diversity, since they are present throughout the planet. At the same time, they are distinguished from the other eukaryotic kingdoms by lacking chlorophyll (they do not photosynthesis) and cell wall (present in cells plants and fungi), as well as their almost entirely sexual reproduction and their ability to movement autonomous and voluntary.

Around two million different species belong to the animal kingdom around the world, grouped into various taxa or phyla, and into two broad categories: vertebrates and invertebrates. In this kingdom, in addition, the human being.

Origin of the animal kingdom

Some sea sponges could even date back 600 million years.

The first animals on the planet appeared during the so-called “Cambrian explosion” 540 million years ago, which consisted of an astonishing diversification and proliferation of the life (especially of multicellular life or metazoans) in the seas of the Earth primitive. The reasons that triggered such an evolutionary "boom" are unknown, but some possible culprits would be the proliferation of oxygen as a result of the dominant plant life, as well as the pressures exerted by volcanic and geochemical activity.

The first animal species were sea sponges, some of which could date as far back as 600 million years, according to ongoing studies. But since then animals have had a strong presence in the fossil record, as they proliferated in the seas and then on land and across the airs.

Characteristics of the animal kingdom

The metabolism of animals cannot produce its own food.

The fundamental characteristics of the animal kingdom can be summarized as follows:

  • They are polycellular and tissue eukaryotic organisms. This means that the bodies of animals are made up of tissues that, in turn, are made up of various types of cells organized among themselves. Even the smallest animals have a body composed of numerous cells, and these are of the eukaryotic type: they have a defined cell nucleus, in which the cell is contained. Genetic information of the individual. These cells also lack chloroplasts and cell walls.
  • They are heterotrophic and of aerobic metabolism. The metabolism of animals cannot produce their own food as plants do, so they must consume organic matter from other living creatures to survive. Bliss organic material it is digested until obtaining its essential nutrients and from it obtaining glucose, a biochemical molecule that will then be oxidized to obtain energy (ATP) that supports the body while walking. This oxidation occurs through the breathing: oxygen is taken from the air or Water (depending on the species) and is released CO2.
  • They have their own mobility.This is one of the main distinctive features of animals: they can move at will, either in water, air or land, using specialized limbs: wings, fins, legs, legs. Thanks to this they can change habitat and look for a more propitious one, escape from predators or chase their prey.
  • They have symmetrical bodies. The bodies of animals can present two types of symmetry, that is, they can be divided into two identical halves. The first is bilateral symmetry (the body is divided longitudinally) and the second is radial symmetry (the body is divided based on its radius, since it is circular).
  • They practice sexual reproduction. With some specific exceptions, in the case of animals capable of parthenogenesis, the animal species reproduce sexually, that is, through the copulation of two individuals of opposite sex (male and female) and the exchange of gametes or sex cells endowed with half of the individual's genetic load, and which also have notably different sizes and shapes.
  • Collagen structured bodies. Unlike other forms of life whose bodies are mainly composed of cellulose, animals have as protein structural collagen.

Animal classification

Vertebrate animals are those that have a skull and a backbone.

In principle, the animal kingdom can be classified into two large groups: vertebrates (62,000 species) and invertebrates (95% of the total species). As its name implies, vertebrates are those that have a skull and a vertebral column or spine, made up of vertebrae; while invertebrates are those that do not have an articulated internal skeleton.

Other forms of classification attend to the specific habitat of the animals, being able to distinguish between marine animals (from the sea and the oceans), aquifers (freshwater), terrestrial (from the mainland), flying (from the air), amphibians (of mixed life between water and land), parasitic (those who live inside the body of others) or urban (of the town).

Taxonomy of the animal kingdom

Mollusks have a soft body and their habitat is mainly aquatic.

The animal kingdom comprises a vast number of phyla or groups of species that share a well-defined body organization, among which the following stand out:

  • Poriferous. About 9,000 species of immobile, benthic and pore inhalant sponges.
  • Cnidarians. About 10,000 species of simple, primitive aquatic animals endowed with stinging tentacles and sac-like bodies.
  • Acanthocephalus. A phylum of 1,100 species of parasitic worms, whose bodies range from a few millimeters to 65 cm.
  • Annelids. Around 16,700 species of worm-bodied invertebrate animals, segmented into rings.
  • Arthropods A gigantic phylum of more than 1,200,000 described species of invertebrates endowed with chitin exoskeletons and jointed limbs, such as insects, crustaceans, arachnids and myriapods. They are the most numerous edge of the kingdom.
  • Brachiopods. Around 16,000 species of marine animals equipped with two shells or shells, with which they protect their soft bodies, similar to mollusks. They are usually immobile.
  • Bryozoans. A set of up to 5,700 species of marine animals (a few are freshwater) that live a fixed life and have a tentacular crown to capture food by filtering the water.
  • Chordates Around 65,000 species of vertebrate animals, possessing a dorsal cord of cells, of which the majority are fish, but which also include birds, mammals Y reptiles.
  • Echinoderms. Marine and benthic animals, of which some 7,000 current species are known, include sea urchins, starfish and the like.
  • Mollusks. Another of the great phyla of the kingdom, includes 100,000 living species of invertebrate animals, soft-bodied and mainly aquatic habitat, among which are octopuses, clams, slugs, etc.
  • Nematodes. A phylum of worms that encompasses more than 25,000 species, commonly called round or cylindrical worms, and account for 90% of life in the relief oceanic.
  • Flatworms. The so-called "flat worms" are about 20,000 species of hermaphroditic animals of aquatic environments or wet, many of which lead a parasitic life.

It would be necessary here to list many other phyla of numerous animal species, the differences of which can be very specific.

Importance of the animal kingdom

The animal kingdom is not only a source of food but also an object of study.

The animal kingdom is one of the most studied and one of the first to be formulated, since human interest in animals dates back to ancient times. Not only as a source of food, or of raw Materials usable, but also as a source of knowledge biological that allows answering fundamental questions about the origin of life, the dynamics of the living body or the maintenance of the ecological cycle that allows a diverse, vast and beautiful world.

Examples from the animal kingdom

Some simple examples from the animal kingdom are:

  • The domestic animals: the dog, the cat, the hamster, the birds, the mice.
  • Insects and arthropodsFrom spiders, scorpions and centipedes, to crabs, scale insects, lobsters and the enormous diversity of insects: mosquitoes, flies, beetles, mantises, cockroaches, bees, etc.
  • Marine animals such as fish, dolphins, sea lions, whales, sharks, mussels, urchins, starfish, but also simpler ones such as zooplankton, jellyfish, etc.
  • Worms in their enormous variety: intestinal parasites, earthworms, crawling worms, etc.
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