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They walk on planet earth long before men, there are hundreds of thousands of species on them, and although we believe we know them, they are still a mystery in their behavior, biology, and diversity, we are talking about animals.
In this article, we will try to answer questions such as: What is the definition of animal? What does the word animal mean? What are animals? How many animal species are there? How are they classified? What are their characteristics? What types of animals are there?
What are animals?
When we classify living beings, we do it mainly in two types: plants and animals.
Animals are those living beings capable of moving, and lacking chlorophyll and cell walls, that is, they are very different from plants as we can see.
Men are included within the group of animals, although unlike these they have the ability to think at the highest level.
Main characteristics of animals
Here are the main or general characteristics of the animals:
- Its cellular organization can be of the eukaryotic or multicellular type.
- In the nutritional aspect, they are heterotrophic beings by ingestion, which is done in one way or another depending on the animal.
- All animals are anaerobic metabolism, meaning they breathe oxygen and can not live without it
- Another characteristic common to all animals is that they reproduce sexually, with a male and a female animal usually found in the process.
- They are also symmetrical beings, except for, for example, sponges. By having symmetry they present a regular arrangement of the different parts or structures of their body along one or more body axes. The symmetry is a radial type or bilateral type.
Exceptions to certain species, the vast majority of animals have muscles and a nervous system capable of sending and processing signals throughout the body.
In addition, all animals perform these vital functions, such as feeding, breathing, circulation, excretion, response, movement, and reproduction.
Types of animals
Animals can be classified and differentiated in several ways. We can classify them according to their type of diet, their way of being born, by having or not a spinal column or by the environment in which they live and develop.
You can also establish a classification according to their natural habits, although it is not the most used, we will also develop it.
Classification by its vertebral structure
Animals may or may not have a spine. Those animals that have a backbone are classified as Vertebrates, while those without a backbone are Invertebrates.
Vertebrate animals are those that have a spine and that have a complex bone structure. Its parts are composed and defined by extremities, trunk, and head…
The vertebrate animals have their body and their skin covered, either by the hair, in the case of most terrestrial animals, feathers in the case of birds, or scales in the case of fish and some species of reptiles. Amphibians mostly have bare skin which is moist.
It is estimated that there are currently more than 62,000 species of vertebrate animals. The vertebrate animals can be classified and divided into five main groups: mammals, fish, birds, reptiles, and amphibians.
Mammals ( Read more on the types of Mammals ) make up a large part of terrestrial animals. What sets them apart from other vertebrates is that they are usually covered and protected by hair.
In most species, females have breasts that allow them to generate milk to breastfeed or feed their young since they are newborns until they are at an age where they can search and digest their food on their own.
Quality of all mammals is their jaw since they possess what is known as a dental bone. It is also a characteristic of almost all species of mammals, including humans, to have bones in the inner part of the ear, called a hammer, anvil, and stirrup.
A characteristic of mammals is what is known as thermal homeostasis. This characteristic of mammals allows them to regulate the temperature and blood flow, with the aim of maintaining an average internal temperature in their body, without changing directly depending on the temperature of the environment.
Fish ( Read more on the types of fishes )differ from vertebrate animals in that they have breathing mechanisms underwater through the gills, through which they absorb oxygen dissolved in water.
They have scales covering their body and have fins instead of limbs, which allow them to move in the aquatic environment. Unlike mammals, fish regulate their internal temperature and that of blood, depending on the temperature present in their environment, which is called ectothermic.
Birds are warm-blooded living beings, which have an internal bone structure with upper and lower extremities, as well as the vertebral column.
They can jump and walk, although their lower extremities are not specially developed for this task, and are more prominent for their ability to fly thanks to their wings, although not all birds can use their wings to fly and some can only achieve great jumps with them (for example chickens).
In most species, its body is covered with feathers with different colors and textures, some even have designs with camouflage capacity as protection against their predators. The form of reproduction of the birds is through eggs and incubation.
Reptiles (Read more on the types of reptiles) are vertebrate animals whose body is mainly covered with scales in the form of protection. They have powerful limbs and a reproduction system using eggs with eggshells.
They have adapted to terrestrial life and have developed defense mechanisms, good lungs, and camouflage, in addition to a double circulatory blood system, in which a blood circuit circulates blood to the lungs specifically and another circuit to the rest of the body.
Reptiles have the ability to regulate their internal temperature adapting to heat sources that are in their environment externally, that is, they are ectothermic, so to warm up their body lies in the sun for several hours, while for cool down require shelter in the shade or in hiding places.
Most reptiles are carnivores and have a simple digestive system for their food.
One of the characteristics of amphibians ( Read more on the types of amphibians )that is especially unique and striking, is that while they are in their larval phase, have a type of breathing similar to that of fish and can breathe underwater, while when they reach adulthood, develop terrestrial pulmonary respiration.
Some amphibians have developed complex defense mechanisms to combat their predators. For example, many of them have poisonous glands in the skin, which can be detected due to the color of the skin, how much stronger or more striking it is, more developed are said glands and more powerful its poison.
This is what is referred to as aposematic coloration or “warning” coloration.
Invertebrate animals, unlike vertebrates, are those that do not have a bone structure or spine.
Many of these animals are small, and have shells as a home and protection, as they are very vulnerable. By not being organized with a bone structure, it is not possible to identify the parts of your body in this way.
Many species of invertebrate animals are protected by bony shells or shells, or by having an external structure called an exoskeleton.
They represent approximately 95% of all animal species on planet earth and do not have the ability to colonize or adapt.
They have adapted to all livelihoods, in underwater environments and even in high-altitude environments. They are very old species and the most numerous forms of life on the planet. Invertebrate living beings are made up of groups and classes that contain thousands of species, such as porphyry, cnidarians, mollusks, annelids, echinoderms, and arthropods.
Classification according to your diet
There are three primary forms of feeding in which we can differentiate and classify animals: Herbivores, Carnivores and Omnivores.
They are those whose main food consists of plants, vegetables, herbs, fruits, and derivatives mainly of plants and vegetation.
It is possible that some species of animals have more orientation to ingest principally or prefer a particular food, although, in the great majority, herbivores feed on a wide variety of leaves, fruits, and plants of all kinds.
Within the classification of herbivorous animals, there are three types we have those called frugivores, which are those that feed mainly on fruit, and those that are called folivore, which feeds especially on leaves. The diet of these animals is usually a bit variable throughout the year depending on the area and seasons. The last type is xylophages they eat only wood.
Although the main food source of the herbivorous animals is the vegetables and their derivatives, many of them also feed on sources of animal protein, such as milk in the case of mammals.
Carnivorous animals are those that base their main diet on meat. They are the ones that make up the dominant part of the food chain.
Its daily nutritional contribution is based on the consumption of meat in two ways: predation or carrion. In predation, animals stalk their prey in groups or individually and perform the attack on a common goal. The scavenger animals, mainly take advantage of the remains of the prey left by the predators once they finish consuming their desired food.
There are carnivores, as is the case with hyenas, who carry out predatory group hunting and also take advantage of carrion, even stealing food from other predators.
There are also animals that have their particular classification and are those that only take care of the depredation of certain animals or specific species, as is the case of the ophiophagus, which are those animals that only feed on snakes.
Omnivorous animals are those that feed on plants and plants as well as animals and insects. Your stomach is not specially designed to digest a particular food group. The human being, in a general way, is classified as Omnivore.
Classification according to its form of reproduction
We can classify animals according to their way of reproduction and birth in three ways: Ovoviviparous, Oviparous and Viviparous or Placenta.
The animals with ovoviviparous reproduction, are those that develop inside an egg, which in turn is inside the uterus of the female, and remains there until the embryo is fully developed.
At the time of delivery, the female gives birth, and the egg can hatch at that moment or just be totally outside the uterus at that moment.
Many reptiles or animals, such as sharks, have this type of reproduction.
In the case of oviparous, contrary to the previous one, the animal lays the egg without the embryo being developed, and it develops over several days. It is necessary for the egg to obtain heat constantly through the process called “incubation”.
The viviparous are all those whose species develop a uterine cavity within the womb of the female where the embryo will develop, receiving all the nutrients and oxygen for it.
The most developed viviparous is called placenta, which is those that give birth to the baby once it is fully developed.
The least developed are the marsupials, which the females after giving birth, continue connected to their offspring and continue to provide nutrients and protection, while still developing in the marsupial pouch or marsupial. One of the clearest examples of this is the case of the kangaroo.
Classification by means of life
We can classify their animals according to the livelihood or their natural habitat, to which they have adapted to survive, develop and reproduce. Three main means of life are established: terrestrial, aquatic and aerial.
They are all those whose natural habitat is in the terrestrial environment and live and develop on the mainland. They find all the necessary means for their survival and are physiologically adapted for life in this environment. They breathe oxygen from the air through their lungs and find their food in their terrestrial habitat.
Among terrestrial animals, we can find from mammals to reptiles and amphibians, even birds that are not able to fly, such as the ostrich or the hen, so it is a means of life varied in species of all kinds.
Aquatic animals are those who spend their whole life, or most of it, in the water, this being their natural livelihood.
Some animals, like most fish, have developed breathing systems that absorb oxygen dissolved in the water through gills, while others, such as dolphins, need to breathe to the surface and take oxygen from the air.
Among aquatic animals, we can classify fish, certain kinds of mammals, birds, and amphibians, and even reptiles, which spend most of their lives in water, so it is also another very varied way of life in species of all.
Aerial animals are those that have the ability to fly and move through the air. They have a light bone structure since most of their bones are hollow, muscles of the chest area well developed and an aerodynamic body and low weight, which allows them to fly with great power and even great speed.
They have a horny beak and have a digestive system that allows them to disintegrate and digest food since they do not have a denture.
Each species has its flight technique, in addition to which some adapt to certain specific zones according to the aerial conditions, and choose this means for its development.
It is the medium in which the smallest number of variety of species is found since it only includes birds identified with the physiological capacities mentioned, some types of flying insects and a single mammal: the bat.
Classification according to natural habits
Although it is not an official way to classify them, we can easily recognize certain species of animals according to their natural habits.
Although today many species have lost at some point their primary naturalness, or have been adapted in some way to change their habits, it is generally divided into three groups: wild, farm and domestic.
- Wild Animals: are those that develop in environments of freedom and in the natural habitat with those of their species. It is possible to find wild animals in all regions, especially in some continents or areas such as the African Savanna or the Amazon Rainforest.
- Farm animals: farm animals are those that have adapted to rural-wild life conditions, although dependent on the human being, in order to take advantage of the resources that can be obtained from them.
- Pets : pets are domestic animals and usually have a very strong affective relationship with people in their known environment. In addition to providing company, many pets are essential for purposes such as guidance, health, and safety.