Informative Text on Animals

Informative Text on Animals

A glimpse into the complex world of animals

When we speak of an animal, we are referring to a living organism endowed with very specific characteristics, shared by all those who, such as human beings, we are part of animal Kingdom, that is, of Regnum animalia, in traditional scientific terms: one of the five kingdoms of known life. The science that studies animals is the zoology.

From a technical point of view, an animal is a multicellular living being (that is, composed of many cells), eukaryote (that is, these cells have an identifiable nucleus) and heterotroph (that is, it feeds on organic material from other living beings), generally endowed with its own mobility and dependent on oxygen consumption (that is, all animals breathe).

It is a group of living beings very vast and very diverse, closely related to the mushroom kingdom (Regnum fungi), which emerged on Earth around 542 and 530 million years ago, in the so-called “Cambrian explosion”: a major event of proliferation and diversification of life that took place in the seas from the Cambrian period.

In this kingdom it covers 20% of the life that exists today on the planet (which is equivalent to only 1% of all the animal species that have existed throughout history), that is, almost a million and a half from species different described, grouped in different categories depending on the shape of their bodies and certain fundamental features. These categories, however, have varied over time as we learn more and more about animals.

The first biologists in the 18th century proposed only six categories to classify all animal species, but today there are estimated to be 32 categories (phyla, from the Latin phylum) recognized to organize all known animal life. All these phyla, however, can be organized into two large groups, depending on whether or not their species present an internal skeleton similar to ours: the vertebrates and the invertebrates, respectively.

The biological classification of the animal kingdom is the subject of continuous study and discussion, but they are popularly used for it. certain historical categories (not scientifically exact), which are more or less useful to differentiate them in life everyday. We usually talk about:

• The mammals. They are those animals that are given birth by their mothers at the end of pregnancy (that is, they are viviparous) and are fed by her through breast milk. Some examples are humans, cows, horses, and elephants.
• The birds. They are animals with a light and feathered body, endowed with wings and a hard beak without teeth. They are usually capable of flight and reproduce by laying eggs (that is, they are oviparous). Some examples are chickens, ostriches, condors, crows, and magpies.
• The reptiles. They are closely related to birds. They are animals with a cold and scaly body, incapable of regulating temperature of their body and that they reproduce by laying eggs (oviparism). Some examples are snakes, crocodiles, iguanas, turtles, and geckos.
• Arthropods. They are very numerous and small animals, equipped with jointed legs and bodies with an external skeleton, which reproduce by laying eggs. Some examples are fleas, mosquitoes, butterflies, spiders, scorpions, among others.
• Amphibians. They are terrestrial animals that reproduce in water and spend the first part of their lives in it until a metamorphosis It allows them to discard the gills and obtain lungs in exchange, moving from the aquatic habitat to the terrestrial one. Some examples are frogs, toads, salamanders, etc.
• Annelids (or worms). They are animals with an elongated and segmented body, both those with a cylindrical body and those with a flat body. Some examples are worms and leeches.
• Fish. They are the quintessential aquatic animals, endowed with gills to filter oxygen from the water and scaled bodies shaped like a torpedo. They reproduce by laying eggs and may have bony or cartilaginous skeletons. Some examples are sardines, tuna, and clownfish.

However, this classification leaves out many animal species and allows a wide margin of confusion between one group and another. Today specialists prefer a broader and more comprehensive general classification, attending to the minimum essential features of the species. Therefore, it is also possible to understand the vastness of the animal kingdom based on two major fundamental groups:

• Animals with bilateral symmetry. They have a body that can be divided along a vertical axis and obtain two symmetrical halves: a right and a left, as is the case with the human body.
• Animals with radial symmetry. They have bodies that are round or tubular and, therefore, when intersected with an imaginary line they produce two equal segments, as long as it is done as the diameter of a circle is drawn. Such is the case, for example, of sea urchins.

Whatever their type, animals are creatures with great evolutionary success, adapted to absolutely all habitats of the planet where oxygen is present. This is because all animals breathe, that is, they consume oxygen from the environment and expel carbon dioxide in return. The oxygen obtained in this way is used to oxidize the sugars that are incorporated in the ingestion of organic matter, and thus make the chemical energy necessary for vital functions.

Now, to get this organic matter, animals can resort to four different strategies, depending on the species:

• Herbivorous animals. They get their food from plants and its by-products, be it the leaves, stems, seeds, barks, roots, flowers, fruits or even the sap. This is the case, for example, of animals such as ox, giraffe or horse, but also of numerous species of birds and of insects.
• Carnivorous animals. Instead, they are predators of other animals, be these herbivores or of another type. These animals have specialized methods and bodies to hunt other animals and consume their meat, from which they obtain the nutrients what do you need. This is the case of the lion, the shark or the praying mantis.
• Omnivorous animals. Also called opportunists, they are those who have a diverse diet based on what the occasion allows: they can hunt animals Small or larger but injured animals can eat eggs or young of other species, but also consume fruits, fungi and vegetables. The best example of this is human beings.
• Detritophagous or decomposing animals. For their part, they are those that feed on decomposing organic matter, that is, waste. These residues can be the carrion left by carnivores, the defecations of larger animals or simply the plant matter that falls and decomposes. This is the case of many species of insects and vultures, scavengers par excellence.

Herbivores, predators, detritophages and omnivores coexist in the different ecosystems and they remain in a tense population balance. They form a cycle of energy and matter transmission from one species to another, as they compete for the resources necessary to survive. And that competition is also the engine of the evolutionary forces that create new species, better adapted to the challenges of their environment.

References:

• "Informative text" in Wikipedia.
• "Animalia" in Wikipedia.
• "The animals" in the Canary Islands Government (Spain).
• "The animals" (video) in The Eduteca.
• "Animal Kingdom" in BYJU’s Classes.
• "Animal (organism)" in The Encyclopaedia Britannica.

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